Institutio Oratoria

Nay, even extempore eloquence, in my opinion, depends on no mental activity so much as memory. For while we are saying one thing, we must be considering something else that we are going to say: consequently, since the mind is always looking ahead, it is continually in search of something which is more remote: on the other hand, whatever it discovers, it deposits by some mysterious process in the safe-keeping of memory, which acts as a transmitting agent and hands on to the delivery

I do not conceive, however, that I need dwell upon the question of the precise function of memory, although many hold the view that certain impressions are made upon the mind, analogous to those which a signet-ring makes on wax. Nor, again, shall I be so credulous, in view of the fact that the retentiveness or slowness of the memory depends upon our physical condition, as to venture to allot a special art to memory.

My inclination is rather to marvel at its powers of reproducing and presenting a number of remote facts after so long an interval, and, what is more, of so doing not merely when we seek for such facts, but even at times of its own accord, and not only in our waking moments, but even when we are sunk in sleep.