Concerning the meaning of the terms, Necessity, Impossibility, Inability, &c. and of Contingence.
When discussing free will, words such as “necessary” and “impossible” are used frequently. Therefore, we must understand exactly how they are used.
We could say that something is necessary if “it must be and cannot be otherwise.” But unless we also explain the word “must” with something other than the phrase “there being Necessity” the phrase above is not a proper definition of Necessity. Words such as “must,” “can,” or “cannot” need to be analyzed just as much as “necessary” and “impossible.”
In everyday use, the word “necessary” is a relative term. To say that something is necessary is to say that it is (or will be) regardless of any supposed opposition to its existence. This is the same as saying that it is impossible for the thing not to exist. But the word “impossible” is also a relative term, referring to an effort to make something happen which turns out to be insufficient to bring it to pass. “Irresistible” is another relative term referring to a resistance made against some force or power which is insufficient to withstand the power or hinder its effect. Necessity and Impossibility imply something that frustrates endeavor or desire. Note the following.
1. Things are necessary in general if they exist or will come to pass regardless of any opposition. A thing is necessary to us if it exists or will come to pass regardless of any opposition from us.
2. Terms such as “necessary,” “impossible,” etc. are most appropriate to discussion about liberty and moral agency (in the sense just described of a thing being necessary/impossible to us regardless of any possible opposition by us).
3. In common usage, “necessity” is a relative term that always supposes some sort of opposition. So when we say something is necessary to us, we mean in relation to some opposition of our Wills, or some effort of ours to the contrary. The only sense in which we can say we make opposition to an event is in our voluntary opposition to it. Something is necessary as to us when, even if we do not want it or do not act to prevent it, the thing is or will be anyway. Our opposition is the opposition our wills (or implies as much).
It is plain that other similar words and phrases are commonly understood the same way. We say that something is impossible for us if we want it or try to make it happen, but our desires and efforts are or would be to no avail. We call something irresistible when all our opposition or efforts to the contrary are overcome. We say we are unable to do something when “our supposable desires and endeavors are insufficient.”
We grow up having learned to understand all of these terms as having a strong connection “to a supposed will, desire, and endeavor of ours.” The connection is so strong that they can never be separated. Certainly, all of these words can be used as terms of art, but unless we are very careful we will unconsciously slide back into the common usage of these words and we will apply them inconsistently in our line of reasoning, “even when we pretend to use them as terms of art.”
4. Therefore, when words such as “necessary,” “impossible,” “irresistible,” etc. are used in cases that do not suppose an insufficient will, they are not being used according to their proper meaning. To use them in such cases is to use them nonsensically. An example of this misuse would be as follows: it is necessary for a man to choose virtue rather than vice during the time that he prefers virtue to vice; and it is impossible for him not to have this choice “so long as this choice continues.” In this example, the words “necessary,” “impossible,” etc. are used either with insignificance or outside their usual sense. Their common meaning (as discussed above) refers to some kind of unwillingness or resistance, but here those things are excluded, “for the case supposed is that of being willing, and choosing.”
5. Thus, it appears that philosophers use words like “necessary” or “impossible” differently from the way they are used in everyday speech, by applying them to cases in which there is no supposable opposition. They use them “with respect to God’s existence before the creation of the world, when there was no other being.” They use them in the context of God’s loving himself, his loving righteousness, or his hating sin. They apply them to the actions of “created intelligent beings,” even in cases where it is supposed that “all opposition of the Will is excluded.”
“Metaphysical or philosophical Necessity is nothing different from their certainty.” By “certainty” I refer to “the certainty that is in things themselves” rather than to a “certainty of knowledge.” It is the former that provides the foundation for the latter.
Philosophical necessity is sometimes defined as “where by it cannot be otherwise.” This is a faulty definition for two reasons. First, the words “can” and “cannot” need just as much explanation as the word “necessity.” So if someone asks us what we mean by saying “it cannot be otherwise,” we might explain by saying “it must necessarily be so.” Second, “this definition is liable to the fore-mentioned great inconvenience.” The words “cannot” or “unable” are relative–they are connected to a power that is or may be exerted “in order to the thing spoken of.” But as already noted, philosophers do not use the word “necessity” in that way.