In philosophy of science, on the other hand, evidence is understood as that which confirms or disconfirms scientific hypotheses and arbitrates between competing theories.
[2] Restricting evidence to conscious mental states has the implausible consequence that many simple everyday beliefs would be unjustified.
This is why it is more common to hold that all kinds of mental states, including stored but currently unconscious beliefs, can act as evidence.
This position has problems in explaining why it is still rational for the subject to believe that there is a fire even though the olfactory experience cannot be considered evidence.
[6][2] In philosophy of science, evidence is understood as that which confirms or disconfirms scientific hypotheses and arbitrates between competing theories.
For scientific consensus, it is central that evidence is public and uncontroversial, like observable physical objects or events and unlike private mental states.
[2][14] Thomas Kuhn is an important advocate of the position that theory-ladenness concerning scientific paradigms plays a central role in science.
[17] It is usually seen as excluding purely intellectual experiences, like rational insights or intuitions used to justify basic logical or mathematical principles.
[19] There is an active debate in contemporary philosophy of science as to what should be regarded as observable or empirical in contrast to unobservable or merely theoretical objects.
[18][27] For example, the proposition that "all bachelors are unmarried" is knowable a priori since its truth only depends on the meanings of the words used in the expression.
[28] Immanuel Kant held that the difference between a posteriori and a priori is tantamount to the distinction between empirical and non-empirical knowledge.
The paradigmatic justification of knowledge a posteriori consists in sensory experience, but other mental phenomena, like memory or introspection, are also usually included in it.
[18] But purely intellectual experiences, like rational insights or intuitions used to justify basic logical or mathematical principles, are normally excluded from it.
[18][27] In its strictest sense, empiricism is the view that all knowledge is based on experience or that all epistemic justification arises from empirical evidence.
This stands in contrast to the rationalist view, which holds that some knowledge is independent of experience, either because it is innate or because it is justified by reason or rational reflection alone.
[35][2] One difficulty for empiricists is to account for the justification of knowledge pertaining to fields like mathematics and logic, for example, that 3 is a prime number or that modus ponens is a valid form of deduction.
[30][35] Such cases have prompted empiricists to allow for certain forms of knowledge a priori, for example, concerning tautologies or relations between our concepts.
[43] The idea behind this distinction is that only experimentation involves manipulation or intervention: phenomena are actively created instead of being passively observed.
[44][45][46] For example, inserting viral DNA into a bacterium is a form of experimentation while studying planetary orbits through a telescope belongs to mere observation.
[47] In these cases, the mutated DNA was actively produced by the biologist while the planetary orbits are independent of the astronomer observing them.
Normally, this validation is achieved by the scientific method of forming a hypothesis, experimental design, peer review, reproduction of results, conference presentation, and journal publication.