In the preceding chapters we have seen that the individual is able to experience sensations in consciousness, and that he is able to _perceive_ them mentally, the latter being the first step in intellectual activity. We have also seen that he is able to reproduce the perception by means of memory and imagination, and that by means of the latter he is able to re-combine and rearrange the objects of perception. We have also seen that he has what are known as "feelings," which depend upon his previous experience and that of his progenitors. So far the mind has been considered merely as a receiving and reproducing instrument, with the added attachment of the re-combining power of the imagination. Up to this point the mind may be compared to the phonographic cylinder, with an attachment capable of re-combining its recorded impressions. The impressions are received and perceived, are stored away, are reproduced, and by the use of the imagination are re-combined. Up to this point the mind is seen to be more or less of an automatic, instinctive faculty. It may be traced from the purely reflex activity of the lowest forms of life up through the lower animals, step by step, until a very high degree of mental power is perceived in animals like the horse, dog, or elephant. But there is something lacking. There is missing that peculiar power of thinking in symbols and abstract conceptions which distinguishes the human race and which is closely bound up with the faculty of language or expressing thoughts in words. The comparatively high mental process of the lower animals is dwarfed by the human faculty of "thinking." And _thinking_ is the manifestation of the intellect. What is it to _think_? Strange to say, very few persons can answer this question correctly at first. They find themselves inclined to answer the inquiry in the words of the child: "Why, to think is to _think_!" Let us see if we can make it plain. The dictionary definition is a little too technical to be of much use to the beginner, but here it is: "To employ any of the intellectual powers except that of simple perception through the senses." But what are the "intellectual powers" so employed, and how are they employed? Let us see. Stating the matter plainly in common terms, we may say that "thinking" is the mental process of (1) comparing our perceptions of things with each other, noting the points of likeness and of difference; (2) classifying them according to the ascertained likeness or difference, and thus tying them up in mental bundles with each set of "things of a kind" in its own bundle; (3) forming the abstract, symbolic mental idea (concept) of each class of things, so grouped, which we may afterward use as we use figures in mathematical calculations; (4) using these concepts in order to form _inferences_, that is, to reason from the known to the unknown, and to form judgments regarding things; (5) comparing these judgments and deducing higher judgments from them; and so on.