But why not, it may be said--why not cut the knot, and set the question at rest, by admitting at once that every man _does_, popularly speaking, believe in the existence of matter, and that he practically walks in the light of that belief during every moment of his life? This observation tempts us into a digression, and we shall yield to the temptation. The problem of perception admits of being treated in _three_ several ways: _first_, we may ignore it altogether,--we may refuse to entertain it at all; or, _secondly_, we may discuss it in the manner just proposed--we may lay it down as gospel that everyman does believe in the existence of matter, and acts at all times upon this conviction, and we may expatiate diffusely over these smooth truths; or, _thirdly_, we may follow and contemplate the subtle and often perplexed windings which reason takes in working her way through the problem--a problem which, though apparently clearer than the noonday sun, is really darker than the mysteries of Erebus. In short, we may _speculate_ the problem. In grappling with it, we may trust ourselves to the mighty current of _thinking_, with all its whirling eddies,--certain that if our thinking be genuine objective thinking, which deals with nothing but _ascertained_ facts--it will bring us at last into the haven of truth. We now propose to consider which of these modes of treating the problem is the best; we shall begin by making a few remarks upon the _second_, for it was this which brought us to a stand, and seduced us into the present digression. It is, no doubt, perfectly true, that we all believe in the existence of matter, and that we all act up to this belief. But surely that statement is not a thing, to be put into a book and _sold_. It is not even a thing which one man is entitled to tell _gratuitously_ to another man who knows it just as well as he does. It must be admitted upon a moment's reflection, that to communicate such information is to trifle with people's patience in an intolerable degree, is to trespass most abominably upon public or upon private indulgence. What, then, shall we say, when we find this kind of truth not only gravely imparted, but vehemently reiterated and enforced by scientific men, as it is in the pages of Dr Reid and other celebrated expounders of the philosophy of the human mind? We shall only say, that the economy of science is less understood than that of commerce; and that while material articles, such as air and sunshine, which are accessible to all, are for that reason excluded from the market of trade, many intellectual wares, which are at least equally accessible, are most preposterously permitted to have a place in the market of science. Such wares are the instinctive principles of Dr Reid. To inform a man that the material universe exists, and that he believes in its existence, is to take for granted that he is an idiot.