5. So familiar are mankind with this distinction, so distinctly marked is it in their minds, that in familiar intercourse, when no particular theory of the mental powers is in contemplation, they are accustomed to speak of the Intellect, Sensibility, and Will, and of their respective phenomena, as entirely distinct from one another. Take a single example from Scripture. "What I shall _choose_, I wot not--having a _desire_ to depart." Here the Apostle evidently speaks of _desire_ and _choice_ as phenomena differing in kind, and not in degree. "If you engage his heart" [his feelings], says Lord Chesterfield, speaking of a foreign minister, "you have a fair chance of imposing upon his _understanding_, and determining his Will." "_His Will_," says another writer, speaking of the insane, "is no longer restrained by his _Judgment_, but driven madly on by his passions." "When wit is overruled by _Will_, And Will is led by fond _Desire_, Then _Reason_ may as well be still, As speaking, kindle greater fire."[1] In all the above extracts the tri-unity of the mental powers, as consisting of the Intellect, Sensibility, and Will, is distinctly recognized. Yet the writers had, at the time, no particular theory of mental philosophy in contemplation. They speak of a distinction of the mental faculties which all understand and recognize as real, as soon as suggested to their minds. The above considerations are abundantly sufficient to verify the three-fold distinction above made, of mental phenomena and powers. Two suggestions arise here which demand special attention. 1. To confound either of these distinct powers of the mind with either of the others, as has been done by several philosophers of eminence, in respect to the Will and Sensibility, is a capital error in mental science. If one faculty is confounded with another, the fundamental characteristics of the former will of course be confounded with the same characteristics of the latter. Thus the worst forms of error will be introduced not only into philosophy, but theology, too, as far as the latter science is influenced by the former. What would be thought of a treatise on mental science, in which the Will should be confounded with the Intelligence, and in which _thinking_ and _willing_ would be consequently represented as phenomena identical in kind? This would be an error no more capital, no more glaring, no more distinctly contradicted by fundamental phenomena, than the confounding of the Will with the Sensibility.