considered in the things or ideas which are the objects of our understanding, is a necessary agreement or disagreement of one part of our knowledge with another: as applied to the mind, it is the perception of such agreement or disagreement; or such a firm well-grounded assent, as excludes not only all manner of doubt, but all conceivable possibility of a mistake.

There are three sorts of certitude, or assurance, according to the different natures and circumstances of things.

1. A physical or natural certitude, which depends upon the evidence of sense; as that I see such or such a colour, or hear such or such a sound: no body questions the truth of this, where the organs, the medium, and the object are rightly disposed.

2. Mathematical certitude is that arising from mathematical evidence; such is, that the three angles of a triangle are equal to two right ones.

3. Moral certitude is that founded on moral evidence, and is frequently equivalent to a mathematical one; as that there was formerly such an emperor as Julius Caesar, and that he wrote the Commentaries which pass under his name; because the historians of these times have recorded it, and no man has ever disproved it since: this affords a moral certitude, in common sense so great, that one would be thought a fool or a madman for denying it.