However, would deductivism be true from a normative perspective?
This is a question that relates with the fundamental question that a principle would be justifiable from a deductivist perspective: if H - hypothesis is the best explanation for the fact or facts that are to be explained, is it reasonable to accept H. As being valid? We will not go into a discussion on what reasonable might mean and what can actually be considered being reasonable. However, in my opinion the answer to such a question could be 'no'. We can accept H. As being reasonable, but I don't think we can accept H. As being valid. On the other hand, deductivism in scientific methodology does not necessarily propose 100% valid statements and hypothesis, but hypothesis that can be worked with.
Is this enough for a scientific hypothesis? Again, this is a difficult question to answer. On a highly likely scale, it also greatly depends on how valid the hypothesis needs to be in the scientific framework in which it is being used. Quite often, one can use an operational hypothesis rather than a valid one and this can be enough to generate a valid hypothesis later on.
Many, including Musgrane, have argued that conclusiveness is not necessarily directly impacting the validity of the premise. In other words, the simple fact that there are not conclusive elements to support the hypothesis does not necessarily make it invalid or not a sufficient reason not to take into consideration the initial premise.
This is partially true, the problem appears that we seemed to have used the same argumentation when denying inductivism its capacity to act as a scientific methodology. Indeed, inductivism was denied and deductivism preferred exactly because it was vulnerable to new observations and not valid because of that. Similarly, deductivism is not conclusive either.
The problem I see in Musgrave's interpretation and support for deductivism is that he argues that even if there is no evidence to probabilistically support the hypothesis, it does not necessarily mean that it is not true. In other words, he argues that rationality can also accept evidence-transcendent beliefs. In my opinion, this is not something that can go hand in hand with the scientific method, which needs to rely on facts to support theories and hypothesis. Additionally, I don't think it is something rational and can lead, in fact, to irrational explanations of facts.
On the other hand, the lack of conclusiveness or finiteness should most likely not disavow the usefulness of deductivism as an introspective towards scientific method. In science, one has to agree that there are theories that do not encompass the entire scientific spectrum. The best example in this sense related Einstein's theory of relativity with Planck's research into the microcosm and his study of quantum mechanics.
In Einstein's case, his theories best present the macrospace and work when applied to the movement of large objects in space, to planets etc. Planck's theories best work when applied to microspace. However, the two theories, both deductively created, do not deny one another, but, in fact, complete each other by covering two perspectives of things. Their validity, in this case, is not limited by their applicability and I think this is also a very important thing to take into consideration when discussing deductivism and its applicability and relationship with the scientific method.
Here we have two different theories, both valid in their own framework, but invalid when applied to the others' framework and set of premises. There validity however has been proven given the distinct premises they have worked with. Can we support, in this sense, the idea that deductivism works as a scientific method applied within a limited applicability range, but without contradicting the statements we have previously made on this subject?
Science in general and physics in particular has not yet discovered a hypothesis or theory that can successfully justify events in different of its areas. Even more so, this is probably a direct consequence of the fact that premises sometimes differ in validity, depending on the different segments of the materialistic approach. The framework can make a certain premise valid in one system, but invalid in another system. This is true in the previously mentioned theories laid out by Planck and Einstein, but also in thermodynamics or electricity theories, for example.
This can go even to the same branches of a particular science, for example geometry. Euclid has stated, based on his postulates, that the sum of the angles in a triangle is exactly 180 degrees. On the other hand, non-Euclidians such as Riemann stated that it is either less or more than that. The reasoning behind these different deductive approaches comes from the initial premises: Euclid uses his fifth postulate, while Riemann does not include its validity in his own research, which means that his final deductive process leads to a different conclusion.
The reason I have mentioned this is because it is easier to understand lack of conclusiveness that deductivism brings to scientific method and still see why deductivism is still a valid approach. Rationality can be seen as a limited concept itself and something rational in one system can become irrational when the system is changed without this affecting the initial rationality in any way. I think that, from that perspective, we can also extrapolate deductivism and argue that it can be successful as a scientific method even if the number of experiments will be limited.
One of the problem that can be found in deductivism as a successful scientific method is the nature of the premises on which the entire deductive process is based and the obvious question of how we can actually determine the premises with which we start the deductive process, given the fact that the premises themselves cannot be actually deducted from anything else, but represent the initial phase of the deductive process.
In my opinion, this is not an argument that can make us deviate from the support of deductivism as a scientific method. The facts that a deductive mechanism starts with are evidentiary facts, facts on which one can agree on in an uncontroversial manner and facts that can constitute reasonable and valid premises of our deductive mechanism.
Another important shortage of deductivism as a scientific method comes from the fact that deductivism does not lead to a theory being confirmed. The experiments and tests do no necessarily show that the theory is 100% valid, but only that these experiments corroborate the initial hypothesis. Despite the debate we have had so far, can we actually state that a scientific method, which needs to be as close to 100% valid as possible, can rely on a deductive methodology which does not assure this in any way?
In my opinion, the tests are varied enough to make this a reasonable mechanism, functional, as a scientific method. The internal tests of a hypothesis assure that it is a consistent and coherent hypothesis/theory, as well as that it is a theory that is consistent with other existing theories.
As Popper mentioned, this is the testing part where deductive logic is sufficient to test the hypothesis. On the other hand, the external tests ensure two things: (1) if the experiments give out observations that do not support the theory, then the theory is false; (2) if the experiments lead to predicted consequences, then the theory is not false. It does not mean that it is necessarily true, but, at this point, it is not false, which means that it could be true.
The number of positive results from experimentation will increase the level of confidence about future predictions of a certain theory, as well as the probability that this theory is valid. Deductivism provides the correct mechanism for this level of confidence in future predictions to increase.
The more experiments and tests we use on a certain hypothesis, the closer to a valid statement we can transform the initial hypothesis. In deductivism, a theory can be improved, its deductive phases can be worked on so as to better fit the scientific evidence and match the results of the experimentation process.
From this perspective, we can probably argue that deductivism is more dynamic than inductivism and that it has a rigorous capacity to improve the initial theory. In the case of scientific methodology, this is probably something that can work in its favor, given the fact that science is based on facts and results and these reflect the validity of a theory.
As we can see from this extensive presentation of both philosophical facts related to the basis of deductivism and to the connection between deductivism and scientific method, as well as the reliability of deductivism as part of scientific method and the impact it can have, although the arguments can go both ways, deductivism seems to be a logical framework, with the correct feedback and control mechanisms to function as a valid scientific mechanism and…