sábado, 31 de marzo de 2007

Hempel’s General Ideas On Philosophy Of Science


The paradox of confirmation of the raven involves the confirmation of the generalization “all ravens are black” by an observation of something that satisfies the logical equivalent statement “all non-black things are non-ravens”, like a red apple, or a white handkerchief . These consequences are paradoxical, but Hempel argues, they must be accepted as valid. My point is that even something satisfies the two conditions non-black non raven it isn’t a confirmation of the generalization “all ravens are black”, a fact may be consistent with the hypothesis or even be an instance of it, without being evidence for it.

Degree Of Confirmation

This concept reflects the assumption which might be called the statistical version of the principle of induction and implies that the relative frequencies observed in the ‘past’ will remain fairly stable in the ‘future’. What degree of confirmation shall be assigned to H on the basis of E? And is represented such as ‘dc (H, E)‘. If a fixed frequency distribution ∆ is given or hypothetically assumed, then it is possible to define the concept pr ( H, E, ∆ ) the probability of H relatively to E according to the distribution ∆, defining dc (H, E)= pr ( H, E, ∆ ). This is an empirical reconstruction of the concept of degree of confirmation On the basis of a given Evidence, we infer the optimum distribution ∆ and then assign to H, as its degree of confirmation the probability which H possesses relatively to E according to ∆ .

Science doesn’t aim al high probabilities, it aims at a high informative content, based on experience, a hypothesis may be very probable because it may tell us very little, a high degree of probability is not an indication of a confirmation it may be only low informative content. Other point in contrast with this confirmation view is that it's based almost exclusively on frequencies of observations, this leaves out many other considerations, such as the previous knowledge on the subject, and its role in confirming the hypothesis.

Hempel on Theories

Hempel defined a theory as :”a coherent, integrated set of statements containing: (1) internal principles, (2) bridge principles, and (3) an identifiable body of phenomena to be explained”

First we have a understood vocabulary, according to the phenomena we’ll be able to state some empirical laws We introduce a new vocabulary, the internal principles to state laws describing the phenomena. The bridge principles are introduced in order to explain our empirical laws which allow us to establish logical connections between statements cast in the vocabulary of our new theory and statements cast in our antecedently understood vocabulary.

Although I agree with Lakato’s proposal of Scientific Research Programs, these are composed of theories which are composed of principles and this arrangement that Hempel describes of theories seems appropriate and important because verisimilitude and fallibility are ideas that are applied to theories and cannot be applied to research programs, but are indeed necessary for the qualification of those into progressive or degenerating.

Scientific Explanation

To Carl Hempel, scientific explanation is an argument that offers reasons for a given phenomenon to happen. It has to satisfied three requirements: explanatory relevance, which means that the explanation “affords good grounds for believing that the phenomenon to be explained did, or does, indeed occur.” Testability, the statement explaining the phenomena must be open to empirical test, and the premises must contain a scientific law.

The set of premises that explains the phenomenon is called the explanans; the conclusion is the phenomenon to be explained and is called the explanandum, it can be a singular fact or a general law. There are two explanans subclasses; one contains sentences which state specific antecedent conditions, the other represent general laws.

Hempel’s claim is that (a) every correct scientific explanation conforms to either the Deductive-Nomological model, D/N or the Inductive-Statistical model, I/S and that (b) anything that conforms to either of these models is a correct scientific explanation . These two models have very similar conditions:

• The explanation must be a deductively valid argument in the D/N model, so that the explanans must entail the explanandum. In the I/S model, the explanandum follows from the explanans with high inductive probability.
• In the D/N model the law-like statements in the explanans state actual laws. In the I/S model the explanans must contain at least one statistical law.
• The explanans must have empirical content.
• The premises contained in the explanans must be true or highly confirmed by all the relevant evidence available.
• And in the case of the I/S model the law must be “maximally specific”.

The second condition is the one which primarily distinguish them, and is also the one which is more debatable, in the case of the DN-model laws and law-like statements are conceptions that limit the scope for explanation, and in the case of the I/S model the statistical laws seem to not be enough for a proper explanation, natural laws make an explanation more accurate instead statistical laws make explanations doubtful. Other fault in which the two models fail is that they don’t properly reflect causal connections, they leave out significant considerations about the role of causality in explanation.

Hempel believed that science evolved in a continuous manner. New theory did not contradict past theory, more comprehensive theory replaced compatible, older theory. Each successive theory's explanation was closer to the truth than the theory before. It was the truth, and the prediction and control that came with it, that was the goal of logical-empirical science. In his view of progress Hempel denies the fact that some theories that have been defeated are false, and are not included in the theories by which were defeated. I believed that science evolves making progress with respect to truth, that is discovering new facts, and making predictions, in this way I agree with Hempel’s view.

viernes, 30 de marzo de 2007

Feyerabend's critics

Feyerabend's papers

Within of papers of Feyerabend, the historical process are very important in the development of knowledge, the history is inherent to knowledge. The actual education “alienates” to individual and it suppress the progress of science. Further, the dominant society and influential groups delay the progress of science and knowledge. The best form of progress in the knowledge is the Anarchy. “For a changing universe and it without established conditions, diversity of theories and methods”. If we clung to this, we do looses other forms potentially “useful” of discovery and analysis. No all theories is quite certain (true), if we postulates new hypothesis and theories that “confirms” or increases the support of the theories already established, we explain about same things and we don't contribute to knowledge. What it does not explain the theory is the start point of new searches. New paths implies new terms (dialectic), thus he concluded that the knowledge must be acquired for pluralistic methodologies. The best method to make science is contrainductive (falsationism). Alternative hypothesis must be proposed and it must be contrasted. Many hypothesis are necessary for a major covering of the reality. The principle of consistency is debated. A theory not must be “confirmed”, it must be “contrasted” with other(s). Theories cannot be dogmas, they are denied or ignore hypothesis potentially falsifiying. Plurality of opinion is advisable for the objective knowledge. Also the critical view of past is main in the science. Not to the scientific chauvinism. In the search of knowledge is necessary the imagination and creativity, however, any statement or sentence cannot be taken as valid in the knowledge, it must be analysed carefully. Because the imagination and observations are linked to our senses (subjective), we must be create new conceptual frameworks to analyze the phenomena and data, about this, he stated that the concepts are related to theories that explain them. The phenomena in reality are linked to their conceptual framework and they can mean different according to a particular view point (Feyerabend, 1965). Feyerabend postulated that is possible to make science “without experience” (1969), however, it does not possible because the data always are linked to experience (historical or sensitive). Thus, Paul Feyerabend proposed a plurality of opinion in the search of knowledge; but with a contrastation of theories and hypothesis sensu Lakatos. In his book Against the method (1975), Feyerabend claims for a “anarchy” in the science, nevertheless, he assume that the best form to acquire knowledge is the contrastation of theories, this goes against which it proposes.

Trough his life, Feyerabend modified many of his affirmations in their papers, therefore, he stated different and contradictory affirmations and ideas which were reformulated after, among they the science without experience and the importance of creativity and imagination. About this, he wrote after in 1987 (Critical Inquiry): “The conceited view that some humans beings, having the divine gift of creativity, can rebuild creation to fit their fantasies without consulting nature and without asking the rest of us, has not only led to tremendous social, ecological, and personal problems, it also has very doubtful credentials, scientifically speaking.” However, his perspective about the philosophy of science is valid because it always will be linked to historical process and political prejudices, etc. Without the history we does not develop knowledge and it is important in the explication of the world (which is historical).

In the history, the different events influences of the individual's life and groups of research. To Feyerabend, it was important because the sociological phenomena press the science to search new paths towards the knowledge. He critics hardly the institutions and methodologies which denies the diversity of opinion and those that delay the “progress” too. I agree with Feyerabend in these ideas because those situation happened in the scientific world.

Paul Karl Feyerabend (January 13, 1924 to February 1994) was philosopher of science best known for his work as a professor of philosophy at the University of California, Berkeley, where he worked for three decades (1958-1989). His major works include Against Method (published in 1975), Science in a Free Society (published in 1978) and Farewell to Reason (a collection of papers published in 1987). Feyerabend became famous for his purportedly anarchistic view of science and his rejection of the existence of universal methodological rules. He is an influential figure in the philosophy of science, and also in the sociology of scientific knowledge.

jueves, 29 de marzo de 2007

Historicity of Science

The “essay” does not have quotations to make the reading easier, but at the end is the bibliography read for writing this.

Popper on 1982 on his book realism and the aim of science tells us that a method of looking for verifications, it’s a typical method of a pseudoscience, and it is clearly different and distinguishable from the method of testing a theory as severely, that is the method of criticism, the method of looking for falsifying instances. If we accept this, the astronomers that look for new stars or that work specifying their distances, are not scientists; but the people that look for falsifying instances for the Chinese zodiac are. Opposite to this, Kuhn shows us that the problem of demarcation is not really a problem, but a product of the human idiosyncrasy; that is why we recognize some problems as scientific while others not depending on the prevailing paradigm. So we could say that the paradigm is what identifies a field of science.

There are two typical parts in science, one of Normal Science and one of crisis. The first one is characterized by past realizations accepted by a community (as a paradigm), for some time, as fundamental for the posterior practice. While normal science could be alone for long time periods, the crisis needs the existence of a paradigm to the emergent theories compete with. Crisis is always prowling around the research, because every problem that normal science sees as a puzzle can be seen, from another perspective, as a counter instance and thus a source of crisis. To my point of view what is important here is how strong and at the same time flexible is the paradigm to support and let the phenomenon being explain with the construct on hand.

The Normal Science focuses its investigation on three principal points. (i)The events that the paradigm has shown as particularly revealing of the things in nature, (ii) the predictions, and (iii) the empirical work undertaken to clear or articulate the theory of the paradigm. During this time the researchers design experiments and technology looking for better measures, and most important the predictions done around the paradigm. This part of the science is important because we need a theoretical body, which allows us to select and evaluate our researches.

The crisis starts with the discovering of a new sort of phenomenon (anomalies), this is a complex process which involves recognizing that something is and what it is. The first is to recognize that something has gone wrong in ways that may prove consequential. But anomalies do not emerge from the normal course of scientific research until both instruments and concepts have developed sufficiently to make their emergence likely and to make the anomaly which results recognizable as a violation of expectation. The second part is the struggle to make the anomaly law-like (because of the slant to physics of Kuhn, I think it could be used theory better). This period demands additional observation or experimentation as well repeated cogitation; while it continues scientists repeatedly revise their expectations, usually their instrumental standards, and sometimes their most fundamental theories as well.

When we are sure that we have an anomaly (unexpected discovery), we need a new vocabulary and new concepts for analyzing events. These new terms made the theories incomparable and the only criteria that could be used to choose between them is what and how they explain about the phenomena interest us.

The crises are resolved in one of three ways. Normal science can prove capable of handing the crisis provoking a problem; that is explaining from the paradigm or pasting to it. Alternatively, the problem resists and is labeled, but it is perceived as resulting from the field’s failure to possess the necessary tools with which it solve it, and so scientists set it aside for a future generation with more developed tools. In a few cases, a new candidate for paradigm emerges, and a struggle over its acceptance ensures; when the new paradigm is accepted and the other abandon a Revolution born. I think there could be another scenario in which the battle does not end in the death, absorbance or postpone of one theory, but the maintenance of both as different research programs or as a very long struggle.

The success of a paradigm is at the beginning a successful promise distinguishable in selected examples and still uncompleted. The Normal Science it about the promise achieve, expanding the knowledge and the facts that the paradigm shows as particularly interesting and revelators, incrementing the fitting extension between the events and the predictions of the paradigm.

The important thing to me about Kuhn thinking is no the Historical Structure of Science, or the importance of the revolution, its that clarify us that we need a conceptual body to develop the knowledge, and it is not as Popper said a process of trial and error, but a process of check and recheck.

- Kuhn T. 1962. Historical Structure of Scientific Discovery. Science 136: 760-764.
- Kuhn T. 1982. Commensurability, Comparability, Communicability. Proceedings of the Biennial Meeting of the Philosophy of Science Association 2: 669-688.
- Kuhn T. 1962. La estructura de las Revoluciones científicas.
- Popper K. 1982. Realism and the Aim of Science.

Methodology of Scientific Research Programs

Imre Lakatos, 1978

An adequately rational reconstruction of science has to evaluate as scientific not a single theory but instead of it a group of interrelated theories; Lakatos called them scientific research programs, which are composed of a conventionally accepted ‘hard core’ of interacting theories and a ‘belt’ of protective auxiliary hypotheses, and proposed the sophisticated falsationism as a criterion to select between rival programs. I agree with that methodology and I am going to present some reasons to support this position.

First at all, the statements which are inconsistent with the program can not defeat it. The program has a heuristic that allows us to save the program: we modify the belt without changing the hardcore; in this way, we can always reconcile the theories and the factual propositions. With sufficient resourcefulness and some luck, we can defend any program for a long time, even if it is false. Mere ‘falsifications’ must not imply rejection; they are to be considered –to convert them in corroborating examples- but need not be acted upon. The pattern of trial –by hypothesis- and error –shown by experiment-, is to be abandoned because no experiment is crucial to defeat a program.

Due to the fact that a program can not be defeated by the anomalies, the only way to decide when to abandon a program is the construction of a better one, which means that it has an excess empirical content over its predecessors, some of which is subsequently verified. As a consequence of this we have rival programs. If a program explains more than the rival, the latter will be falsified; therefore, the falsationism –a sophisticated one- requires competing programs. The competition is significant and leads to a rational reconstruction of scientific change in which each rival try to increase its content and predict novel facts. On the other hand, no advantage for one side can ever be regarded as absolutely conclusive; a novel belt of auxiliary hypotheses can strengthen a program. Consequently, the heuristic allows us to continue working in a program, as a positive outcome of that we won’t reject a program if the anomalies take place, giving us the opportunity to look at the potential of it.

Even though we can modify the belt of auxiliary hypotheses, there is a difference between the scientific modifications and the pseudoscientific ones that we make. A research program is said to be progressing –and therefore scientific- as long as its theoretical growth anticipates its empirical growth, that is, as long as it keeps predicting novel facts with some success. Conversely, a research program is said to be degenerating –and consequently, pseudoscientific- if it gives only a reinterpretation –a linguistic one- of facts anticipated, and discovered in a rival program. According to this methodology the greatest scientific achievement are research programs which can be evaluated in terms of progressive and degenerating problem shifts.

Another fundamental point is that the methodology of scientific research programs has a historical character. If we wan to follow this methodology and develop a scientific program we will look in history for rival research programs and if instead of it we want to explain different speeds of development of different research program we may need to invoke external history. Moreover, the scientific revolutions along the history are shifts of one program over another.

We need a lot of time to evaluate a research program, but this evaluation is stricter because it requires that the belt of auxiliary hypotheses –following a positive heuristic- turn into a progressive shift and predicts novel facts. The methodology of research programs, finally, emphasizes long-extended theoretical and empirical competition of major research programs, progressive and degenerating problem-shifts, and the slowly emerging victory of one program over the other.

miércoles, 28 de marzo de 2007

The Evolutionary Species Concept

E. O. Wiley and Richard L. Mayden

An evolutionary species is an entity of organisms that maintains its identity from other such entities through time and over space and that has its own independent evolutionary fate and historical tendencies. Species are lineages, ontological individuals existing though time and bounded by speciation events.

The evolutionary species are logical individuals with origins, existence and ends. They are tokogenetic entities that function in the phylogenic system as the analog of phylogenetic entities, clades. Sexual species may show cohesion patterns such that the tokogenetic relationship among the organisms are not well correlated with, or are uncorrelated with, any hierarchical relationships that might exist among those organisms. On the other hand, asexual species have tokogenetic relationships that are similar to multicellular individual organisms in being composed of tokogenetic clone vectors descended from a single ancestor.

The evolutionary species maintain their identities, which refers to the reestablishment of the tokogenetic network when subsequent sympatry occurs between populations that had been allopatric. Particular species are the result of historical processes and then we have discovered them during the course of our research. They have independent tendencies which imply that they are free to vary and evolve independent of their sister species. They also have an evolutionary fate which means that the species are real entities and not a result of our imagination; their fate is to speciate or eventually goes extinct.

If the monophyletic groups have objective reality through time, the ancestral lineage and all descendants of that lineage also must have objective reality. The fact that we can reconstruct much of the phylogenetic histories of groups constitutes evidence that independently evolving lineages exist in nature. Another proof that such lineages do exist is derived from the fact that phylogenetic analysis becomes complicated when lineage independence is not strictly maintained.

The evolutionary species concept is the logical analog of the concept of the monophyletic group, therefore it is a strictly genealogical and non-operational concept. Lastly, all evolutionary species are comparable because they are the largest tokogenetic biological system, consequently general phenomena associated with speciation can be studied even among non-sister species.

The phylogenetic Species Concept (sensu Mishler and Thriot): Monophyly, Apomorphy, and Phylogenetic Species Concepts.

Brent D. Mishler and Edward C. Theriot.

A species is the least inclusive taxon recognized in a formal phylogenetic classification. As with all hierarchical level of taxa in such a classification organisms are grouped into species because of evidence of monophyly. Taxa are ranked as species rather than at some higher level because they are the smallest monophyletic groups deemed worthy of formal recognition, because of the amount of support for their monophyly and/or because of their importance in biological process operating on the lineage in question

Sensu Mishler and Theriot, there is no species problem per se in systematics. Rather, there is a taxon problem. Once one has decided what taxon names are to represent in general, then species taxa should be the same kinds of things, just the least inclusive. Evolution is real, as are organisms (physiological units), lineages (phylogenetic units), and demes (interbreeding units), for example. On the other hand, our classification systems are obviously human constructs, meant to serve certain purposes of our own: communication, data storage and retrieval, and predictivity. These purposes are best served by classification systems that reflect our best understanding of natural processes of evolution, and the field of systematics in general has settled on restricting the use of formal taxonomic names to represent phylogenetically natural, monophyletic groups.

A phylogenetic systematic study of a previously unknown group of organisms involves three major temporal, logical phases:

1. In the precladistic phase the elements of a cladistic data matrix are assembled. These elements include OTUs (operational taxonomic units), characters, and character states. OTUs are assembled initially from grouping together of individual specimens that are homogeneous for the characters then known. Here is important to stress that there is no obvious, theory-free way to individuate species. The process must involve analysis, and that analysis must be explicitly phylogenetic.

2. Cladistic analysis involves translation of the data matrix into a cladogram. Reciprocal illumination is often involved here as well because incongruence between characters or odd behaviour of particular OTUs may lead to a return to phase 1, a re-examination of OTUs and characters, primarily to check for fit to the assumptions of the cladistic method.

3. Classifications based on an assessment of the relative support for different clades provide a basis for evolutionary studies. Formal taxa (including species) are named here on the basis of clear support for their existence as monophyletic cross sections of a lineage and for their utility in developing and discussing theories.

Any cladistic analysis that fails to take into account the possibility of reticulation may not be realistic. Not all lineages may have evolved apomorphic characteristics, and so they may not be identifiable through character analysis. That is, there may be monophyletic groups for which there is no direct evidence. This is a general problem for cladistic analysis and is not special to the species problem.

Henninian species concept

Modified Hennigian species concept:

A species concept based on the criterion of "reproductive community" alone does not satisfy the demands of strict phylogenetic systematics (Hennig, 1950 against Mayr). Hennig includes the cohesion (gene flow) to define species. The initial concept of Hennig was revitalized by Willmann (1985; 1986).


The modified Hennigian species concept based on reproductive isolation and cohesion through gene flow, because he was interested in the delimitation of species in time (1966). someone support the importance of the cohesion in the delimitation of species; others support the reproductive isolation (Mayr, 1957). The cohesion and reproductive isolation can be applied to the "most inclusive Mendelian population"; but the factor more important is the isolation (reproductive gap).

Agamotaxa are taxa consisting of uniparental organisms originate in a way similar to bisexual species, each agamotaxa is isolated reproductively from all others. The phylogenetics relationships of agamotaxas are different to bisexual populations, the terminals would be organisms individual.

Phylogenetic Justification:

A concept appropriate for phylogenetic systematics must consider the historical dimension of species. The monophyletic groups consist of a stem species and all their descendants (Hennig). Species is viewed as a temporal series of populations connecting two speciation events. If we assume monophyly in the Hennigian concept; we assume that the stem species cannot survive speciation, and a species comprise the entire branch segment between two speciation events.

Species Recognition:

A species concept based on reproductive isolation attempts to describe natural entities (Willmann, 1991). The BSC (Biological species concept) and HSC (Hennigian species concept) is not character related and they is identical if absolute isolation is adopted. In allopatric populations, the breeding experiments in a artificial environment determines whether it belong to the same species (Wiley, 1981). the species concepts based on characters does not inferring species boundaries.

Potential and Actual Interbreeding:

The potentiality of interbreeding of the populations is a important factor for the stability of the BSC. However; the HSC modified (Willmann) only is related to reproductive isolation.


The criterion of absolute isolation is not exclude any arbitrariness (Key, 1981; Willmann, 1985). The use from several criteria can be incorrect. The isolation criterion does not interfere with any kind of biological research.

Survival of the Stem Species:

The populations becomes species only relative to their next kin. Speciation creates a pair of news species, and it eliminate the stem species (Willmann, 1989). If we does not assume the dissolution of the stem species, we does denies that species have boundaries in time.

lunes, 19 de marzo de 2007

Biological Species Concept

Ernst Mayr

The Biological Species Concept can be stated as: biological species are groups of interbreeding natural populations that are reproductively isolated from other such groups.

The Biological Species Concept answers the Darwinian Why question, Why are there species? Why do we not find in nature simply an unbroken continuum of similar or more widely diverging organism? An organization of the diversity of life into species permits the protection of harmonious, well balanced, well adapted gene pools, an indiscriminate interbreeding of individuals, would lead to an immediate breakdown of these harmonious genotypes, for this reason the concept is not applicable to organisms that don't form sexual populations, their genotype does not require any protection because it is not threatened by destruction through out crossing.

By what devices is the integrity of a species being maintained? Dobzhansky introduced the term isolating mechanisms for these devices defining them as agents that hinder the interbreeding of groups of individuals or reduces to zero the frequency of exchange of genes between the groups. There is a enormous diversity of such devices : sterility genes, chromosomal incompatibilities, ecological exclusion, behavioral properties that facilitate the recognition of conspecifics.

What a biologist encounters in nature are populations of organism, the task is to assign these populations to species. This requires two operations a.) to develop a concept of what a species is, resulting in the definition of the species category in the Linnean hierarchy an b.) to apply this concept when combining populations into species taxa.

The species taxon refers to a concrete zoological or botanical object consisting of a classifiable population of organism. They are particulars, individuals or biopopulations they can be described and delimited against other species taxa.

The species category indicates a rank in the Linnaean hierarchy, it articulates the concept of the biological species and is defined by the species definition.
Is the species a class or an individual? "The species taxon -any species taxon- is an individual with any member of that particular species being a part of the species. The species category however is a class. It is the class, the species of wich are the species taxa. "(Mayr, 1976)

The criticisms of the Biological Species Concept are directed against the decisitions made in the delimitation of species taxa, in contiguous interbreeding populations it causes no difficulties. However, the criterion of interbreeding would seem to be inapplicable in the delimitation of species wherever isolated populations are involved, populations isolated either in time or space. The basic difficult is that populations isolated evolve as independent gene pools and some of them are on their way to becoming a new species or are actually have passed this threshold. But we must take an inference on the basis of all available data and criteria( analysis of their genetics, molecular biology tools, nature of their isolation mechanism ) as to how far along they have proceed on the way to becoming a separate species. However in most ambiguous situations it is useful to treat allopatric populations of doubtful rank as subspecies , trinomials provide information of closest relationship and allopatry, In ornithology the convention has developed to call strongly differentiated allopatric populations, allospecies.

The biological species concept deal with the definition of the species category , and only has meaning where a gene pool comes into contact with gene pools of other species that is at a given locality and at a given time (the nondimensional situation), However, because species taxa have an extension in space, the species status of noncontiguous populations must be determined by inference. Also species taxa have an extension in time, thus evolving is not such a species criterion, species do not differ in this respect from other living entities.

domingo, 4 de marzo de 2007

Defensa a Popper

‘Science does not aim, primarily, at high probabilities. It aims at a high informative content, well backed by experience. But a hypothesis may be probable simply because it tells us nothing, or very little’ (Popper, 1954).

The inductivism is a logic impossible, just because from observational facts, can not being infer theories. The theories are product of a mental process in which we conjecture about reality. Additionally, is technically impossible to observe the entire Phenomena’s events, because is preferable to look for those events (tests) that falsify the theory.

Popper proposed that the truth content of the theories, even the best of them, cannot be verified by scientific testing, but can only be falsified or corroborated. The knowledge is the result of conjectures (response to a given problem situation) which are systematically subjected to the most rigorous attempts at falsification possible. The conjectures that pass the process of refutation are not more true, but rather, more corroborated and then more applicable to the problem situation at hand. This applicability does not predict continued corroboration; neither does rigorous testing protect a conjecture from refutation in the future. So we can never know in fact when something is true, neither from experience, nor from any other source; we only could be sure about is false.

Popper proposed his formula [C(h,e,b) = p(e,hb)-p(e,b)] as a way to explain in a brief and simple way his science philosophy. The two extremes (1, -1) are unattainable, just because we need that the evidence be probable in some way, and because we can never reach the truth (or be sure we reach it). If we got any number above 0, we corroborate our theory, so what the famous 0.5 lets us is to differentiate between naïve and strong falsationism. From the idea at the beginning, we can say that a naïve test is the one, which does not explain more than the trivial.

If we assume that what is called ‘scientific knowledge’ consists only of guesses or conjectures, then this assumption is sufficient for solving the problem of induction, without sacrificing empiricism; that is to say, without adopting a principle of induction and ascribing to it a priori validity. For guesses are not induced from observations (although they may, of course, be suggested to us by observations.) The key to the solution of inductions problem is the recognition that our theories, even the most important ones, and even those which are actually true, always remain conjectures. And the main points given by Popper to solve inductions problem are:

- Acceptance of the view that theories are of supreme importance
- Acceptance of Hume’s argument against induction: any hope that we may posses positive reasons for believing in our theories is destroyed by that argument
- Acceptance of the principle of empiricism scientific theories are rejected or adopted (tentatively) in the light of the results of experimental or observational tests
- Acceptance of critical rationalism: scientific theories are rejected or adopted as being better or worse than other known theories in the light of the results of rational criticism.

All this steer us to a central point in Popper’s philosophy, the problem of demarcation; and sum we can say that a method of looking for verifications, it’s a typical method of a pseudoscience, and it is clearly different and distinguishable from the method of testing a theory as severely as we can – that is, the method of criticism, the method of looking for falsifying instances.


Elliott Sober
Proceedings and Addresses of the American Philosophical Association, Vol. 73, No. 2. (Nov.,
1999), pp. 47-76.

Nowadays, there is general agreement about the importance of understanding what it takes for a statement to be confirmed or disconfirmed by an observation. There is also a wide consensus that the design of experiments is an important issue; if somebody wants to test a proposition, it is important to make sure that the experiment that is carried out, actually bear on the proposition in question.

Testing is an inherently contrastive activity; and testing a hypothesis requires that it make a prediction that can be checked by observation. We make observations in order to learn about things that we do not observe; these observations must be “theory neutral”, they should be neutral, relative to the competing theories under test.

An empirically soluble problem is one in which the competing hypotheses make different observational predictions. The hypotheses rarely make observational predictions on their own; they require supplementation by auxiliary assumptions if they are to be tested. The problem here is that usually the auxiliary assumptions are looked for, or chosen because the researcher has good reasons to think they are true. This means that the auxiliary assumptions used in a test and the hypotheses under test differ in their epistemological standing. The observational outcomes favour one competing hypothesis over the others. But the test typically will not test the auxiliary assumptions at all. Typically, the auxiliary assumptions are epistemically independent to the test outcome.

Somebody could think that auxiliary assumptions may include idealizations. Nevertheless what is essential is not that one be able to say that a set of assumption is true, but that it is harmless- that correcting the idealization could not affect the conclusion one draws. However, it is not enough just to assert that the idealization is harmless; one must have evidence that this is so.

Finally the author talks about the probability of the hypotheses, and tells us that there is no probabilistic analog of modus tollens. If a hypothesis deductively entails something false, then the hypothesis is false. But if a hypothesis that what you observe was very improbable, what then? It does not follow that the hypothesis it self is improbable. So based on this, we can judge which hypotheses do better and which do worse in their competition, that is all.