Necessity and Time

Necessity and Time

What is the connection between necessity and time? Time is not usually mentioned in discussions of necessity, but it is easy to see that the two notions are logically connected. If a proposition is necessary, then it is true at all times. In fact, it is necessarily true at all times: it can’t be necessary and not true at all times. This holds for analytic necessity and metaphysical necessity (if this table is necessarily made of wood, then it is made of wood for the duration of its existence). Contingent truths, on the other hand, can be true at one time but not at another (the table may be brown at one time and white at another). It is not sufficient to be necessary that the proposition is true at all times, since contingent truths may be always true, but it is necessary. Thus, necessity entails temporal universality. Necessities are not changeable. This is part of our ordinary understanding of necessity. But it is not made explicit in standard treatments of necessity. If we say that necessity is truth in all possible worlds, we can be asked, “Do you mean true in all possible worlds at a given time?” We had better not mean that, since it is possible that at earlier or later times the proposition might not be true; we have to mean “all possible worlds at all times”. So, temporal universality is tacitly assumed—as it must be. The concept of time enters into the concept of necessity. Modal logic is bound up with temporal logic. Modal thinking is connected to temporal thinking. It might even be that the earliest notions of necessity were purely temporal: the necessary is simply what holds at all times and not just some. Then it was noticed that this is not quite strong enough, because some types of necessity require more than temporal universality (contingently true universal quantifications over time). But the concept must contain this kind of temporal fact. The concept of the necessary includes the concept of the eternal. To put it differently, we can infer from a necessary truth how things were in the past and how they will be in the future, whereas we cannot do that for a contingent truth. Necessity gives us vast knowledge of past and future: it will never not be true that 2 + 2 = 4! It’s like a kind of godlike knowledge, enabling us to survey all of history, past and future. Perhaps this is why necessary truth has always been held in high regard, while also suspected of hocus-pocus.

            This aspect of necessity is regularly ignored, but it needs to be recognized if we are to have a full account of the concept. However, in another respect standard treatments say too much: does our concept of necessity really contain a reference to possible worlds? Suppose I say that this table is necessarily made of wood: do I thereby make reference to these very big objects called “worlds” (each as big as the actual world)? Isn’t this an imposition on our ordinary meaning? Doesn’t it over-intellectualize vernacular modal discourse? Surely the only object I refer to when I make my comment about this table is this table: I say that in all possible states of this table it is made of wood. I don’t say anything about worlds that contain multitudes of otherobjects. I refer only to possibilities relating to this table: I say that it, and it alone, must be a certain way (at all times). My ontological commitments do not extend to whole possible worlds, or even to other objects in them. I might not even believe in such entities. So, this concept should be subtracted from our account of the concept of necessity, and the concept of time added to it—not worlds but times.[1]

[1] This is one of those cases in which a certain formal apparatus has been allowed to cloud our vision: we see the quantifier “for all worlds w” and we don’t think much further about the concept it is intended to represent.