We know certainly, by experience, that we SOMETIMES think; and thence draw this infallible consequence,--that there is something in us that has a power to think.
But whether that substance PERPETUALLY thinks or no, we can be no further assured than experience informs us.

For, to say that actual thinking is essential to the soul, and inseparable from it, is to beg what is in question, and not to prove it by reason;--which is necessary to be done, if it be not a self-evident proposition But whether this, "That the soul always thinks," be a self-evident proposition, that everybody assents to at first hearing, I appeal to mankind.

It is doubted whether I thought at all last night or no.

The question being about a matter of fact, it is begging it to bring, as a proof for it, an hypothesis, which is the very thing in dispute: by which way one may prove anything, and it is but supposing that all watches, whilst the balance beats, think, and it is sufficiently proved, and past doubt, that my watch thought all last night.

But he that would not deceive himself, ought to build his hypothesis on matter of fact, and make it out by sensible experience, and not presume on matter of fact, because of his hypothesis, that is, because he supposes it to be so; which way of proving amounts to this, that I must necessarily think all last night, because another supposes I always think, though I myself cannot perceive that I always do so.
But men in love with their opinions may not only suppose what is in question, but allege wrong matter of fact.