Concerning the meaning of the terms, Necessity, Impossibility, Inability, &c. and of Contingence
The words necessary, impossible, &c. are abundantly used in controversies about Free-Will and Moral Agency; and therefore the sense in which they are used should clearly understood.
Here I might say, that a thing is then said to be necessary when it must be, and cannot be otherwise. But this would not properly be a definition of Necessity, any more than I explained the word must, by the phrase, there being a Necessity. The words must, can, and cannot, need explication as much as the words necessary, and impossible; excepting that the former are words that in earliest life we more commonly use.
The word necessary, as used in common speech, is a relative term; and relates to some supposed opposition made to the existence of a thing, which opposition is overcome, or proves insufficient to hinder or alter it. That is necessary, in the original and proper sense of the word, which is, or will be, notwithstanding all supposable opposition. To say, that a thing is necessary, is the same thing as to say, that it is impossible that it should not be. But the word impossible is manifestly a relative term, and has reference to supposed power exerted to bring a thing to pass, which is insufficient for the effect; as the word unable is relative, and has relation to ability, or endeavor, which is insufficient. Also the word irresistible is relative, and has always reference to resistance which is made, or may be made, to some force or power tending to an effect, and is insufficient to withstand the power, or hinder the effect. The common notion of Necessity and Impossibility implies something that frustrates endeavor or desire.
Here several things are to be noted.
1. Things are said to be necessary in general, which are or will be notwithstanding any supposable opposition from whatever quarter. But things are said to be necessary to us, which are or will be notwithstanding all opposition supposable in the case from us. The same may be observed of the word impossible, and other such like terms.
2. These terms necessary, impossible, irresistible, &c. more especially belong to controversies about liberty and moral agency, as used in the latter of the two senses now mentioned, viz. as necessary or impossible to us, and with relation to any supposable opposition or endeavor of ours.
3. As the word Necessity, in its vulgar and common use, is relative, and has always reference to some supposable insufficient opposition; so when we speak of anything as necessary to us, it is with relation to some supposable opposition of our Wills, or some voluntary exertion or effort of ours to the contrary. For we do not properly make opposition to an event, any otherwise than as we voluntarily oppose it. Things are said to be what must be, or necessarily are, as to us, when they are, or will be, though we desire or endeavor the contrary, or try to prevent or remove their existence: but such opposition of ours always either consists in, or implies, opposition of our wills.
It is manifest that all such like words and phrases, as vulgarly used, are understood in this manner. A thing is said to be necessary, when we cannot help it, let us do what we will. So any thing is said to be impossible to us, when we would do it, or would have it brought to pass, and endeavor it; or at least may be supposed to desire and seek it; but all our desires and endeavors are, or would be, vain. And that is said to be irresistible, which overcomes all our opposition, resistance, and endeavor to the contrary. And we are said to be unable to do a thing when our supposable desires and endeavors are insufficient.
We are accustomed, in the common use of language, thus to apply and understand these phrases: we grow up with such a habit; which, by the daily use of these terms from our childhood, becomes fixed and settled; so that the idea of a relation to a supposed will, desire, and endeavor of ours, is strongly connected with these terms, whenever we hear the words used. Such ideas, and these words, are so associated, that they unavoidably go together; one suggests the other, and never can be easily separated as long as we live. And though we use the words, as terms of art, in another sense, yet, unless we are exceedingly circumspect, we shall insensibly slide into the vulgar use of them, and so apply the words in a very inconsistent manner, which will deceive and confound us in our reasonings and discourses, even when we pretend to use them as terms of art.
4. It follows from what has been observed, that when these terms necessary, impossible, irresistible, unable, &c. are used in cases wherein no insufficient will is supposed, or can be supposed, but the very nature of the supposed case itself excludes any opposition, will, or endeavor; they are then not used in their proper signification. The reason is manifest; in such cases we cannot use the words with reference to a supposable opposition, will, or endeavor. And therefore if any man uses these terms in such cases, he either uses them nonsensically, or in some new sense, diverse from their original and proper meaning. As for instance; if any one should affirm after this manner, That it is necessary for a man, or what must be, that he should choose virtue rather than vice, during the time that he prefers virtue to vice; and that it is a thing impossible and irresistible, that it should be otherwise than that he should have this choice, so long as this choice continues; such a one would use the terms must, irresistible, &c. with either perfect insignificance, or in some new sense, diverse from their common use; which is with reference, as has been observed, to supposable opposition, unwillingness, and resistance; whereas, here, the very supposition excludes and denies any such thing: for the case supposed is that of being willing, and choosing.