Stewart. Now Mr Stewart, understanding, as he did, the philosophy of causation, ought to have known that every difficulty as to _how_ one thing gives rise to another, is purely a difficulty of the mind's creation, and not of nature's making, and is, therefore, no difficulty at all. Let us explain this,--a man says he knows _that_ fire explodes gunpowder; but he does not know _how_ or by what means it does this. Suppose, then, he finds out the means, he is still just where he was; he must again ask how or by what means these discovered means explode the gunpowder; and so on _ad infinitum_. Now the mind may quibble with itself for ever, and _make_ what difficulties it pleases in this way; but there is no _real_ difficulty in the case. In considering any sequence, we always know the _how_ or the means as soon as we know the _that_ or the fact. These means may be more proximate or more remote means, but they are invariably given either proximately or remotely along with and in the fact. As soon as we know _that_ fire explodes gunpowder, we know _how_ fire explodes gunpowder,--for fire is itself the means which explodes gunpowder,--the _how_ by which it is ignited. In the same way, _if_ we knew that matter gave rise to perception, there would be no difficulty as to _how_ it did so. Matter would be itself the means which gave rise to perception. We conceive, therefore, that Mr Stewart did not consider what he was saying when he affirmed that Reid's plain statement of facts exhibited _the difficulty_ in all its magnitude. If Reid's statement _be_ a statement of fact, all difficulty vanishes,--the question of perception is relieved from every species of perplexity. If it _be_ the fact that perception is consequent on the presence of matter, Reid must be admitted to have explained, to the satisfaction of all mankind, _how_ perception is brought about. Matter is itself the means by which it is brought about.