a man suffers himself to be reasoned out of the principles of common sense by metaphysical arguments, we call it metaphysical lunacy, which differs from the other species of the distemper in this, that it is not continued, but intermittent; it is apt to seize the patient in solitary and speculative moments; but when he enters into sanity, Common Sense recovers her authority.'
It is the first of these three examples of the common sense that is the subject of the Inquiry—intended as preliminary to others which may follow. 'A clear enumeration and explication of the principles of common sense' was henceforward Reid's ultimate aim; but thus far he took those involved in our experience when we are tasting, or smelling, or hearing, or touching, or seeing. As axioms and definitions are the preliminaries of abstract mathematical reasonings, so our sensuous perceptions through the five senses are the preliminaries to reasonings about concrete realities in the world of change. The leading principle of the Inquiry is, that something extended, solid, and movable is directly manifested in our sensuous experiences, equally with the direct manifestations of our own sensations and other feelings when we are conscious of them; and also that we are obliged by common sense to regard extended, solid, and movable things as other than mere transitory sensation or idea. Extended things, large or small, refuse to be melted down into sensations or states of one’s private consciousness. Take this specimen of philosophical argument for accepting perceptions which cannot be logically demonstrated, but which the common sense of human nature refuses to reject:—
'Suppose I am pricked with a pin, I ask, is the pain I feel a sensation? Undoubtedly it is. There can be nothing that
