Lastly, it cannot be denied that these three acts are all natural to the mind; I mean, that, in exercising them, we are not violating the laws of our nature, as if they were in themselves an extravagance or weakness, but are acting according to it, according to its legitimate constitution. Undoubtedly, it is possible, it is common, in the particular case, to err in the exercise of Doubt, of Inference, and of Assent; that is, we may be withholding a judgment about propositions on which we have the means of coming to some definitive conclusion; or we may be assenting to propositions which we ought to receive only on the credit of their premisses, or again to keep ourselves in suspense about; but such errors of the individual belong to the individual, not to his nature, and cannot avail to forfeit for him his natural right, under proper circumstances, to doubt, or to infer, or to assent. We do but fulfil our nature in doubting, inferring, and assenting; and our duty is, not to abstain from the exercise of any function of our nature, but to do what is in itself right rightly. 3. So far in general:—in this Essay I treat of propositions only in their bearing upon concrete matter, and I am mainly concerned with Assent; with Inference, in its relation to Assent, and only such inference as is not demonstration; with Doubt hardly at all. I dismiss Doubt with one observation. I have here spoken of it simply as a suspense of mind, in which sense of the word, to have “no doubt” about a thesis is equivalent to one or other of the two remaining acts, either to inferring it or else assenting to it. However, the word is often taken to mean the deliberate recognition of a thesis as being uncertain; in this sense Doubt is nothing else than an assent, viz. an assent to a proposition at variance with the thesis, as I have already noticed in the case of Disbelief. Confining myself to the subject of Assent and Inference, I observe two points of contrast between them. The first I have already noted. Assent is unconditional; else, it is not really represented by assertion. Inference is conditional, because a conclusion at least implies the assumption of premisses, and still more, because in concrete matter, on which I am engaged, demonstration is impossible. The second has regard to the apprehension necessary for holding a proposition. We cannot assent to a proposition, without some intelligent apprehension of it; whereas we need not understand it at all in order to infer it. We cannot give our assent to the proposition that “x is z,” till we are told something about one or other of the terms; but we can infer, if “x is y, and y is z, that x is z,” whether we know the meaning of x and z or no. These points of contrast and their results will come before us in due course: here, for a time leaving the consideration of the modes of holding propositions, I proceed to inquire into what is to be understood by apprehending them.