Receptivity
Even Kant was influenced by this perspective and in his Critique of Pure Reason explicitly stressed the receptivity of the senses as opposed to the constructive action of the understanding, and credited the senses with the capability of providing the “intuitions” which (though still remaining ‘internal’ to the knowing subject as pure “appearances” or “phenomena”) offer the indispensable ground for knowledge, because the a priori transcendental conditions for “thinking”—imposed on the phenomena by the structure of the intellectual categories—have only the function of securing to knowledge the indispensable characteristic of universality and necessity.
This is why Kant could declare himself at the same time “empirical realist” and “transcendental idealist”: due to their receptivity the senses—though remaining unable to attain the “things in themselves”—could preserve at least a ‘limited’ independence of the content of knowledge from the knowing activity of the subject.This ingenuous solution, however, opens at least two questions: (i) does receptivity eliminate the risk of subjective bias in knowledge? And (ii) is the specific constitution of the knowing subject an insurmountable obstacle to our cognition of reality? The answer to the first question is negative: the idea that sense perceptions ‘come from' the external world and are ‘received’ by the subject in its own particular way is rather spontaneous for common sense and was defended by various philosophers since antiquity; in medieval Scholastics was even expressed as a general principle: quidquid recipitur ad modum recipientis recipitur (“whatever is received is received in the way of the recipient”). Many philosophers took this fact as the cornerstone of subjectivism: the same food tastes pleasant to a person and unpleasant to another one, or even to the same person when she is healthy and when she is sick, so that flavor is not an intrinsic property of the food, but depends on the receptive subject. The same can be repeated for numberless properties we attribute to reality and for several other kinds of judgments.
Starting with Protagoras and going on during the whole history of Western philosophy this way of thinking supported what we can call an “anti-realist” position in epistemology, which was taken even by thinkers who accepted the idea of the receptivity of the subject not only at the level of sensations, but in cognition in general.On the other hand, one can admit the obvious fact that the constitution of the different sense organs is a necessary condition for knowing certain features of reality: one needs eyes for seeing colors, and ears for hearing sounds. However, one cannot see sounds or hear colors, and this means that every particular sense organ can reveal only certain specific properties of reality. Or, symmetrically, this means that certain properties of reality can be detected only by specific sense organs. This is a “realist” position in epistemology fully compatible with the receptivity of cognition (one could say that the different cognitive capabilities ‘detect’ or ‘give access’ to different aspects of reality). Moreover, it is also possible to maintain that not the receptivity, but the active and constructive parts of cognition are those that offer the ground for saving the universality and necessity of knowledge, thus being the best defense against subjectivism and skepticism. This is notoriously the core of Kant’s “Copernican revolution” in which, instead of assuming that “all our knowledge must conform to objects” it is claimed that “objects must conform to our knowledge”. The reason why this move does not amount to subjectivism is that— according to Kant—the contribution of understanding to knowledge does not consist in representations but in functions that organize sense representations and, moreover, are not capabilities of the individual minds, but universal features of reason, being conditions for thinking as such.
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