1. De Morgan read a paper on the ‘Logic of Relations’ before the Cambridge Philosophical Society, and the paper is printed in their Transactions. He attempts to deal not only with the idea of relationship, but with the idea of relation in general. As he does not deal with exact ideas, he cannot give any exact results.

2. Among the writings of Leslie Ellis there are printed some notes on Boole's ‘Laws of Thought,’ and there he refers to the idea of relation. He makes the important remark:— ‘It seems to me that the mind passes from idea to idea in accordance with various principles of suggestion, and that, in correspondence with the different. classes of such principles of suggestion, we ought to recognise different branches of the general theory of inference.’