After this rather long but necessary preface, we come to the intellectual factor rightly so termed, which we have been little by little approaching. The essential, fundamental element of the creative imagination in the intellectual sphere is the capacity of thinking by analogy; that is, by partial and often accidental resemblance. By analogy we mean an imperfect kind of resemblance: like is a genus of which analogue is a species. Let us examine in some detail the mechanism of this mode of thought in order that we may understand how analogy is, by its very nature, an almost inexhaustible instrument of creation. 1. Analogy may be based solely on the _number of attributes compared_. Let _a b c d e f_ and _r s t u d v_ be two beings or objects, each letter representing symbolically one of the constitutive attributes. It is evident that the analogy between the two is very weak, since there is only one common element, _d_. If the number of the elements common to both increases, the analogy will grow in the same proportion. But the agreement represented above is not infrequent among minds unused to a somewhat severe discipline. A child sees in the moon and stars a mother surrounded by her daughters. The aborigines of Australia called a book "mussel," merely because it opens and shuts like the valves of a shellfish.[10] 2. Analogy may have for its basis the _quality_ or _value_ of the compound attributes. It rests on a variable element, which oscillates from the essential to the accidental, from the reality to the appearance. To the layman, the likeness between cetacians and fishes are great; to the scientist, slight. Here, again, numerous agreements are possible, provided one take no account either of their solidity or their frailty. 3. Lastly, in minds without power, there occurs a semi-unconscious operation that we may call a transfer through the omission of the middle term. There is analogy between _a b c d e_ and _g h a i f_ through the common letter _a_; between _g h a i f_ and _x y f z q_ through the common letter _f_; and finally an analogy becomes established between _a b c d e_ and _x y f z q_ for no other reason than that of their common analogy with _g h a i f_. In the realm of the affective states, transfers of this sort are not at all rare. Analogy, an unstable process, undulating and multiform, gives rise to the most unforeseen and novel groupings. Through its pliability, which is almost unlimited, it produces in equal measure absurd comparisons and very original inventions. After these remarks on the mechanism of thinking by analogy, let us glance at the processes it employs in its creative work. The problem is, apparently, inextricable. Analogies are so numerous, so various, so arbitrary, that we may despair of finding any regularity whatever in creative work. Despite this it seems, however, reducible to two principal types or processes, which are personification, and transformation or metamorphosis.