I shall here use the word to denote an assent, but an assent to a proposition, not as true, but as probably true, that is, to the probability of that which the proposition enunciates; and, as that probability may vary in strength without limit, so may the cogency and moment of the opinion. This account of Opinion may seem to confuse it with Inference; for the strength of an inference varies with its premisses, and is a probability; but the two acts of mind are really distinct. Opinion, as being an assent, is independent of premisses. We have opinions which we never think of defending by argument, though, of course, we think they can be so defended. We are even obstinate in them, or what is called “opinionated,” and may say that we have a right to think just as we please, reason or no reason; whereas Inference is in its nature and by its profession conditional and uncertain. To say that “we shall have a fine hay-harvest if the present weather lasts,” does not come of the same state of mind as, “I am of opinion that we shall have a fine hay-harvest this year.” Opinion, thus explained, has more connexion with Credence than with Inference. It differs from Credence in these two points, viz. that, while Opinion explicitly assents to the probability of a given proposition, Credence is an implicit assent to its truth. It differs from Credence in a third respect, viz. in being a reflex act;—when we take a thing for granted, we have credence in it; when we begin to reflect upon our credence, and to measure, estimate, and modify it, then we are forming an opinion. It is in this sense that Catholics speak of theological opinion, in contrast with faith in dogma. It is much more than an inferential act, but it is distinct from an act of certitude. And this is really the sense which Protestants give to the word, when they interpret it by Conviction; for their highest opinion in religion is, generally speaking, an assent to a probability—as even Butler has been understood or misunderstood to teach,—and therefore consistent with toleration of its contradictory. Opinion, being such as I have described, is a notional assent, for the predicate of the proposition, on which it is exercised, is the abstract word “probable.” 4. _Presumption._ By Presumption I mean an assent to first principles; and by first principles I mean the propositions with which we start in reasoning on any given subject-matter. They are in consequence very numerous, and vary in great measure with the persons who reason, according to their judgment and power of assent, being received by some minds, not by others, and only a few of them received universally. They are all of them notions, not images, because they express what is abstract, not what is individual and from direct experience.