THE CEREBRUM, AND ITS FUNCTIONS. 777 



as its subsequent nutrition (according to the general laws of assimilation, 591) 

 takes place on the same plan, we can understand the well-known force of early 

 associations, and the obstinate persistence of early habits of thought. 



808. But a not less important " tendency to thought/ 7 and one whose opera- 

 tion is more concerned in all the higher exercises of our reasoning faculties, is 

 that which may be expressed under the designation of the Law of Similarity, 

 and which consists in the general fact that any present state of consciousness 

 tends to revive previous states that are similar to it. It is thus that we instinct- 

 ively invest a new object with the attributes we have come to recognize in one 

 that we have previously examined, to which the new object bears such a re- 

 semblance, that the sight of the latter suggests those ideas which our minds 

 connect with the former. Thus, we will suppose a man to have once seen and 

 eaten an orange ; when he sees an orange a second time, although it may be 

 somewhat larger or smaller, somewhat rougher or smoother, somewhat lighter 

 or darker in hue, he recognizes it as an orange, and mentally assigns to it the 

 fragrance and sweetish acidity of the one which he had previously eaten. But 

 if, instead of being yellow, the fruit were green, he would doubt of its being an 

 orange; and if assured that it still was, but had not come to maturity, he would 

 no longer expect to find it sweet, the notion of intense acidity being suggested 

 to his mind by his previous experience of other green and unripe fruit. It is 

 in virtue of this kind of action, that we extend those elementary notions which 

 are primarily excited by sensation, to new objects. Thus, the idea of roundness 

 (like other notions of form) is originally based on the combination of the mus- 

 cular and visual sensations, and must be first acquired by a process of consider- 

 able complexity; but when once derived from the examination of a single object, 

 it is readily extended to other objects of the same character. So, again, it is 

 by the operation of this mental tendency, that we recognize similarity where it 

 exists in the midst of difference, and separate the points of agreement from those 

 of discordance ; and this, again, not merely as regards objects which are before 

 our consciousness at the same time or in close succession, but also with regard 

 to all past states of consciousness. It is thus that we identify and compare, 

 that we lay the foundations of classification, and that we recover all past im- 

 pressions which have anything in common with our present state of conscious- 

 ness. The intensity of this tendency, and the habitual direction which it takes, 

 vary extremely in different individuals. Some have so great an incapacity for 

 recognizing similarity, that they can only perceive it when it is in marked 

 prominence, their minds taking much stronger note of differences; whilst others 

 have a strong bias for the detection of resemblances and analogies, and discover 

 them where ordinary minds cannot recognize them. Some, again, address them- 

 selves to the discovery of similarity among objects of sense, whilst others study 

 only those ideas which are the objects of our internal consciousness ; and it is 

 in the detection of what is essentially similar among the latter, that all the 

 higher operations of the intellect essentially consist. Even here we find that 

 some are contented with superficial analogies, whilst others are not satisfied until 

 they have penetrated by analysis to the depths of the subject, and are able to 

 compare its fundamental idea with others of like kind. It is this habit of mind, 

 which is of essential value in all the sciences of Classification and Induction. 

 Thus, in the formation of generic definitions to include the characters which a 

 number of objects have in common, their subordinate differences being for a 

 time left out of view, we are entirely guided by the recognition of similarity 

 between the objects we are arranging; and the same is the case in the formation 

 of all the higher groups of families, orders, and classes, the points of similarity 

 becoming fewer and fewer as we proceed to the more comprehensive groups, 

 whilst those of difference increase in corresponding proportion. The sagacity of 

 the Naturalist is shown in the selection of the best points of resemblance, as the 



