Thinking makes itself into passive understanding, that is, into what is for it the objective; and thus it here becomes plain to what extent the dictum _nihil est in intellectu quod non fuerit in sensu_ expresses Aristotle’s meaning. Aristotle, raising difficulties, goes on to ask, “If reason is simple and unaffected by impressions, and has nothing in common with other objects, how can it think, since thinking is certainly a state of receptivity?” That is to say, in thinking there is a reference to an object distinct from itself. “For it is when two objects have something in common that the one appears to produce and the other to receive an impression. There is a further difficulty, whether understanding can itself be the object of thought. In that case understanding would either be inherent in other things—unless it is the object of thought in a different sense from that in which other things are so, but there is only one sense in which things can be objects of thought—or, on the other hand, it would have something compounded with it, making it an object of thought as other things are. Now it has been already said that passivity is so determined that understanding is in potentiality all that thought is exercised on: but at the same time it is in actuality nothing before the exercise of thought.” That is to say, thought is implicitly the content of the object of what is thought, and in coming into existence it only coincides with itself; but the self-conscious understanding is not merely implicit, but essentially explicit, since it is within itself all things. That is an idealistic way of expressing it; and yet they say that Aristotle is an empiricist.
The passivity of understanding has therefore here only the sense of potentiality before actuality, and that is the great principle of Aristotle; in regard to this he brings forward at the end of the same chapter another much-decried illustration, which has been just as much misunderstood as the preceding. “Reason is like a book upon whose pages nothing is actually written;” that is, however, paper, but not a book. All Aristotle’s thoughts are overlooked, and only external illustrations such as this are comprehended. A book on which nothing is written everyone can understand. And the technical term is the well-known _tabula rasa_, which is to be found wherever Aristotle is spoken of: Aristotle is said to have alleged that the mind is a blank page, on which characters are first traced by external objects, so that thinking thus comes to it from without.[99] But that is the very opposite of what Aristotle says. Instead of the Notion being adhered to, casual comparisons such as these have been caught up here and there by the imagination, as if they expressed the matter itself. But Aristotle did not in the least intend that the analogy should be pushed to its furthest extent: the understanding is of a surety not a thing, and has not the passivity of a writing-tablet; it is itself the energy, which is not, as it would be in the case of a tablet, external to it. The analogy is therefore confined to this, that the soul has a content only in so far as actual thought is exercised. The soul is this book unwritten on, and the meaning consequently is that the soul is all things implicitly, but it is not in itself this totality; it is like a book that contains all things potentially, but in reality contains nothing before it is written on. Before real activity nothing truly exists; or “Understanding itself can enter thought, like the objects of thought in general. For in that which is without matter” (in mind), “the thinker” (the subjective) “and the thought” (the objective) “are the same; theoretical knowledge and that which comes to be known are the same. In that which is material, thinking is only in potentiality, so that understanding itself does not belong to it; for understanding is a potentiality without matter, but the object of thought exists in it,” while Nature contains the Idea only implicitly. It is plain from this that the above illustration has been taken in quite a false sense, utterly contrary to Aristotle’s meaning.