The first time a man saw the communication of motion by impulse, as by the shock of two billiard balls, he could not pronounce that the one event was _connected_, but only that it was _conjoined_, with the other.
After he has observed several instances of this nature, he then pronounces them to be _connected_.

What alteration has happened to give rise to this new idea of _connexion_?
Nothing but that he now _feels_ those events to be _connected_ in his imagination, and can readily foresee the existence of the one from the appearance of the other.

When we say, therefore, that one object is connected with another we mean only that they have acquired a connexion in our thought, and give rise to this inference, by which they become proofs of each other's existence; a conclusion which is somewhat extraordinary, but which seems founded on sufficient evidence."-- (IV.pp.

87-89.) In the fifteenth section of the third part of the _Treatise_, under the head of the _Rules by which to Judge of Causes and Effects_, Hume gives a sketch of the method of allocating effects to their causes, upon which, so far as I am aware, no improvement was made down to the time of the publication of Mill's _Logic_.

Of Mill's four methods, that of _agreement_ is indicated in the following passage:-- " ...