must be made by definition; for the question is concerning the signification of the name. But if it be asked concerning an abstract name, _what is it?_ the cause is demanded why a thing appears so or so. As if it be asked, _what is hard?_ The answer will be, hard is that, whereof no part gives place, but when the whole gives place. But if it be demanded, _what is hardness?_ a cause must be shewn why a part does not give place, except the whole give place. Wherefore, I define an _accident_ to be _the manner of our conception of body_. [Sidenote: How an accident may be understood to be in its subject.] 3. When an _accident_ is said _to be in a body_, it is not so to be understood, as if any thing were contained in that body; as if, for example, redness were in blood, in the same manner, as blood is in a bloody cloth, that is, as a part in the whole; for so, an accident would be a body also. But, as magnitude, or rest, or motion, is in that which is great, or which resteth, or which is moved, (which, how it is to be understood, every man understands) so also, it is to be understood, that every other accident _is in_ its subject. And this, also, is explicated by _Aristotle_ no otherwise than negatively, namely, that _an accident is in its subject, not as any part thereof, but so as that it may be away, the subject still remaining_; which is right, saving that there are certain accidents which can never perish except the body perish also; for no body can be conceived to be without extension, or without figure. All other accidents, which are not common to all bodies, but peculiar to some only, as _to be at rest_, _to be moved_, _colour_, _hardness_, and the like, do perish continually, and are succeeded by others; yet so, as that the body never perisheth. And as for the opinion that some may have, that all other accidents are not in their bodies in the same manner that extension, motion, rest, or figure, are in the same; for example, that colour, heat, odour, virtue, vice, and the like, are otherwise in them, and, as they say, _inherent_; I desire they would suspend their judgment for the present, and expect a little, till it be found out by ratiocination, whether these very accidents are not also certain motions either of the mind of the perceiver, or of the bodies themselves which are perceived; for in the search of this, a great part of natural philosophy consists. [Sidenote: Magnitude, what it is.] 4. The _extension_ of a body, is the same thing with the _magnitude_ of it, or that which some call _real space_. But this _magnitude_ does not depend upon our cogitation, as imaginary space doth; for this is an effect of our imagination, but _magnitude_ is the cause of it; this is an accident of the mind, that of a body existing out of the mind. [Sidenote: Place, what it is, and that it is immovable.]