11 The Rational Theory
This theory was adopted by a number of prominent European philosophers, such as Descartes,  Kant  and others. It can be summarized in the belief that there are two sources of conceptions. One of them is sense perception. Thus, we conceive ‘heat’, ‘light’, ‘taste’ or ‘sound’ due to our sense perception of all of that. The other is the innate nature. This is to say that the human mind possesses ideas and conceptions that are not derived from the senses, but are fixed in the innermost being of the innate nature. Thus, the soul draws [certain ideas] from itself. According to Descartes, these innate conceptions are the ideas of Cod, the soul, extension and movement, as well as the ideas that resemble them, and are characterized by complete clarity in the human mind. And, according to Kant, the whole field of conceptual human knowledge and science – including the two forms of time and space, as well as the twelve categories,  for which Kant is known – is innate.
The senses are, on the basis of this theory, the source of understanding the simple conceptions and ideas. However, they are not the only source. Rather, there is also the innate nature that produces in the mind a number of conceptions.
What obliged the rationalists to adopt this theory for explaining human conceptions was this. They did not find a reason for the arising of a number of ideas and conceptions from the senses, since they are non-sensible ideas. Thus, they must be derived essentially from the innermost being of the soul. This makes it clear that the philosophical motive for postulating the rational theory would be completely eliminated if we could explain the mental conceptions solidly, and without need of supposing innate ideas. Because of this, we can refute the rational theory in two ways.
The first is by analyzing knowledge in a way that would attribute all of it to the senses, and facilitate understanding the manner in which all conceptions are produced from the senses. Such an analysis would deny any justification to the theory of innate ideas, since it was based on the complete separation of some ideas from the sphere of the senses. Therefore, if it were possible to extend the reach of the senses to the various areas of conception, there would be no need for innate conceptions. This way was adopted by John Locke  in responding to Descartes and other such rationalists. Later, it was also adopted by those who upheld the empirical principle, such as Berkeley  and David Hume. 
The second way is the philosophical method for responding to [the view of] innate conceptions. It is based on the principle that a multiplicity of effects cannot be the result of chat which is simple, by virtue of the fact of its simplicity. The soul is simple. Therefore, it cannot be a cause in a natural manner of a number of conceptions and ideas. Rather, the existence of such a large number of pieces of knowledge in the soul must be caused by many external factors. These factors are the instrumental senses and the various sensations that occur to them.  (p. 68)
A complete criticism of this proof requires that we explain the principle on which it is based, and give a clarification of the reality and simplicity of the soul. But for this, there is no room here. However, we must point out the following. First, this proof – if one can accept it – does not totally demolish the theory of innate ideas, because it only demonstrates the lack of a multiplicity of innate pieces of knowledge, but does not prove that the soul does not naturally possess a limited [number of] conceptions  concordant with its unity and simplicity, and resulting in a number of other conceptions independent of the senses. In the second place, we would like to clarify that if the rational theory means that in the human soul there are innate ideas in actuality, then it becomes possible for the proof presented above to respond to this theory as follows. The soul is simple in essence; so, how could it produce that large number of innate ideas? Indeed, if the rationalists were truly inclined to believe that, then our human inner feeling would be sufficient for rejecting their theory. This is because all of us know that at the moment human beings [begin] to exist on the face of the earth, they do not possess any idea, regardless of how clear and general it is in the human mind:
In light of this interpretation, the rational theory cannot be rejected on the basis of the philosophical demonstration or scientific evidence which has already been mentioned.