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Rh got three. My experiments were not brought to a conclusion, but, if they had been, it would not have been right to assume too readily that the birds knew how to count. We should have to inquire whether I had not involuntarily made some sign manifesting my intention. The remarkable experiments of Mr. Cumberland have revealed to us a whole category of motions of this kind which had never been taken account of before. Who, previous to him, would have suspected that the hand trembles in a different way when we think of seven and when we think of three?

The solution is not advanced, then, when we tell of the cases, curious and interesting as they may be, in which animals seem to behave like man; or, to speak more exactly, these cases are proof only with respect to persons who are inclined to attribute instincts alone to the animal, and deny it reflection and calculation. As the philosophers are still at this point, it may be well to try to undeceive them. Mutatis mutandis, the spider chooses the place for its web, and the bird for its nest, as the colonist selects the location of his farm-house, or of the pen for his goat or pig. I will agree that we may regard the laying of the eggs, the making and shaping of the nest, and the selection of materials as instinctive acts; but the selection of the place is necessarily of a deliberate and intelligent character.

If there is a difference between animal and human intelligence, it depends upon special causes, and these are what we are trying to disentangle. I have already remarked that man has the faculty of thinking by symbols, while the animal appears not to have it. What is a symbol? It is not easy to define the term. Let us say provisionally that it is a conventional mental sign, representing a clear abstraction. The definition is neither very good nor very clear, but it will do, for want of a better one. Before Thales and Pythagoras, thinkers had distinguished between the common idea and the concept. The common idea is formed within us, we may say, almost physiologically. Take, for example, the idea of horse. When I have seen twenty horses, I have seen for twenty times the qualities which they all have in common, while I have seen for a less number of times, or only once, their respective individual qualities; so that the common image engraves itself in the brain or in the sensorium, if that term is preferred, in deeper and deeper lines and stands out strongly at the base of the particular and fugitive images.

The concept partakes of the common idea, and it might perhaps be maintained that it is formed within us in the same manner. But the degree of abstraction which it necessitates is infinitely more considerable. Let it be, for example, the number four. We agree, it is true, that the idea of, say, any group of four fingers of the hand is a kind of common idea; but it is a good way from this idea, from this kind of group, to that of four distant and different objects, like the four limbs, the four largest cities in the world, the first four Roman