28 THE PRINCIPLE OF Chap. I. 



three principles throw light on the theory of the sub- 

 ject. It appears to me that so many expressions are 

 thus explained in a fairly satisfactory manner, that 

 probably all will hereafter be found to come under the 

 same or closely analogous heads. I need hardly pre- 

 mise that movements or changes in any part of the 

 body, — as the wagging of a dog's tail, the drawing back 

 of a horse's ears, the shrugging of a man's shoulders, 

 or the dilatation of the capillary vessels of the skin, — 

 may all equally well serve for expression. The three 

 Principles are as follows. 



I. The principle of serviceable associated Habits. — 

 Certain complex actions are of direct or indirect serv- 

 ice under certain states of the mind, in order to relieve 

 or gratify certain sensations, desires, &c; and when- 

 ever the same state of mind is induced, however feebly, 

 there is a tendency through the force of habit and asso- 

 ciation for the same movements to be performed, though 

 they may not then be of the least use. Some actions 

 ordinarily associated through habit with certain states 

 of the mind may be partially repressed through the 

 will, and in such cases the muscles which are least under 

 the separate control of the will are the most liable still 

 to act, causing movements which we recognize as expres- 

 sive. In certain other cases the checking of one habitual 

 movement requires other slight movements; and these 

 are likewise expressive. 



II. The principle of Antithesis. — Certain states of 

 the mind lead to certain habitual actions, which are of 

 service, as under our first principle. Now when a direct- 

 ly opposite state of mind is induced, there is a strong and 

 involuntary tendency to the performance of movements 

 of a directly opposite nature, though these are of no 

 use; and such movements are in some cases highly ex- 

 pressive. 



