As to causation; we may observe, that the true idea of the human mind, is to consider it as a system of different perceptions or different existences, which are linked together by the relation of cause and effect, and mutually produce, destroy, influence, and modify each other.  Our impressions give rise to their correspondent ideas; said these ideas in their turn produce other impressions.  One thought chaces another, and draws after it a third, by which it is expelled in its turn.  In this respect, I cannot compare the soul more properly to any thing than to a republic or commonwealth, in which the several members are united by the reciprocal ties of government and subordination, and give rise to other persons, who propagate the same republic in the incessant changes of its parts.  And as the same individual republic may not only change its members, but also its laws and constitutions; in like manner the same person may vary his character and disposition, as well as his impressions and ideas, without losing his identity.  Whatever changes he endures, his several parts are still connected by the relation of causation.  And in this view our identity with regard to the passions serves to corroborate that with regard to the imagination, by the making our distant perceptions influence each other, and by giving us a present concern for our past or future pains or pleasures.

As a memory alone acquaints us with the continuance and extent of this succession of perceptions, it is to be considered, upon that account chiefly, as the source of personal identity.  Had we no memory, we never should have any notion of causation, nor consequently of that chain of causes and effects, which constitute our self or person.  But having once acquired this notion of causation from the memory, we can extend the same chain of causes, and consequently the identity of car persons beyond our memory, and can comprehend times, and circumstances, and actions, which we have entirely forgot, but suppose in general to have existed.  For how few of our past actions are there, of which we have any memory?  Who can tell me, for instance, what were his thoughts and actions on the 1st of January 1715, the 11th of March 1719, and the 3rd of August 1733?  Or will he affirm, because he has entirely forgot the incidents of these days, that the present self is not the same person with the self of that time; and by that means overturn all the most established notions of personal identity?  In this view, therefore, memory does not so much produce as discover personal identity, by shewing us the relation of cause and effect among our different perceptions.  It will be incumbent on those, who affirm that memory produces entirely our personal identity, to give a reason why we cm thus extend our identity beyond our memory.