Preliminary Definitions and Illustrations. 3 



the latter case, as a technical term, it has to a large 

 extent lost its freedom and mobility, being bound in the 

 chains of a more or less precise, but at the same time 

 more or less arbitrary, definition. For the purposes of 

 exact science such bondage is necessary ; and there are 

 many words, such as "force," "energy," "impression," 

 " sensation," which we continually use in daily conversation 

 or in general literature with a freedom which would be 

 inadmissible in technical descriptions. Such a word is 

 " instinct." But it unfortunately happens that, whereas 

 physicists are generally agreed among themselves as to the 

 exact meaning which the words " force " and " energy " 

 shall carry as technical terms, naturalists and psychologists 

 are by no means fully agreed * as to the precise sense in 

 which the term " instinct " shall be used. 



There is, moreover, in the case of " instinct," a source 

 of difficulty which is absent in that of the technical terms 

 which are employed in the science of physics. Let us 

 suppose that we are watching a silkworm spinning its 

 cocoon. A set of activities, for the carrying out of which 

 the structure of the caterpillar is admirably adapted, are 

 performed before our eyes, and may be watched in all their 

 stages ; such activities, if they fulfil certain conditions, we 

 term instinctive. But if now we are asked what prompts 

 the silkworm at a certain stage of its existence to spin its 

 cocoon, the reply is that this is due to " instinct." How far 

 such a reply is justifiable we shall have to consider. But 

 it is clear that, in the case of the activities themselves, we 

 are dealing with matters of actual observation ; but if we 

 say that the activities are due to instinct, we are dealing 

 with something which cannot be directly observed, but 

 which we infer to be present. And that which we thus 



* Cf. ■ Some Definitions of Instinct " in Natural Science for May, 1895, 

 vol. vii. p. 321. 



