ing us with a confidence that the result will be worth having. 

 If there is this possibility of misinterpreting purpose within 

 our own species, how careful must we be when we pass to 

 animal behaviour. 



We see a crofter making, year after year, a long line 

 of the stones he has gathered from his field. We infer that 

 he is arranging them so as to be least inconvenient. But 

 one day he digs a trench beside the line and begins to lay 

 the biggest blocks solidly within it. We know that he is 

 going to build a wall. Now it is quite possible that this 

 purpose was not in his mind when he began, and did not 

 arise until the line of stones reached certain dimensions 

 or until his clearance gave him a little leisure to think of a 

 further improvement. This idea of an increasing purpose 

 seems to be of great importance in Natural History, where 

 a secondary end often appears to grow out of a primary 

 one. 



We inferred that the crofter was building a wall because 

 we could not make sense of his activity on any other assump- 

 tion; we argued by analogy from our own experience; and 

 if we knew his language we could verify our interpretation 

 by asking him what he was working towards. He would 

 tell us that he had been working intermittently for years 

 because he had the purpose of building a wall. The thought 

 of the future wall was something actual which moved the 

 crofter to will and to do. The thought and the will were 

 in a real sense the ground of necessity of the wall, not less 

 real than the stones. 



But the convincingness of our interpretation of the crofter's 

 actions as the outcome of his purpose rests, we must admit, 

 on our recognition of him as a fellow-countryman, on his 

 own assurance, and on parallels between his behaviour and 



