Time, metaphysics of

3. Presentism and eternalism

Since the 1990s there has been much debate in the philosophy of time between proponents of presentism (see Presentism) and eternalism. Presentism is a version of the A-theory because it holds that there is a real ontological distinction between past, present and future, and that time’s flow is real. The presentist version of the ontological distinction between past, present and future is the most extreme: only what is present exists; neither past nor future entities exist. For example, according to presentism, Queen Elizabeth II exists, but Queen Elizabeth I does not, and neither does Queen Elizabeth II’s first great-great-grandchild. Eternalism is the opposing view that past and future objects are just as real as present objects. Queen Elizabeth I and Queen Elizabeth II’s first great-great-grandchild are just as real as Queen Elizabeth II herself. Eternalism is, thus, the ontological component of the B-theory. However, it is possible to be an eternalist and an A-theorist, for example, by holding that past (future) objects exist but count as past (future) in virtue of possessing the property of pastness (futurity).

The focus on the presentism / eternalism debate is at least partly explained by the rise in popularity of presentism itself. Perhaps one explanation for this is due to an argument that undermines non-presentist versions of the A-theory (Bourne 2002; Braddon -Mitchell 2004). According to this argument, any theory that assigns ontological privilege to the present moment while also recognizing the existence of non-present times faces an insurmountable problem: it is unable to account for our knowledge that we are located in the present. If anything is certain, surely our knowledge that we are present is! But if past times exist as well as the present time, what is to say we are not located in one of those past times, mistakenly believing ourselves to be present? We might insist that our experience of presentness is so compelling that it must be veridical. But what about Queen Elizabeth I’s experience of presentness? That’s pretty compelling too, yet she is in the past, so her experience misleads her. Perhaps our experience misleads us too.

There are two views of the ontological nature of time that are immune to this argument. They are presentism and the B-theory’s version of eternalism. Presentism avoids the thrust of the argument by denying that there are any nonpresent times that are real. Since only what is present exists, if I exist, I am present. My knowledge that I am present is therefore guaranteed. The B-theory avoids it by denying that the present is ontologically privileged. My knowledge that I am present is nothing more than the indexical knowledge that I am located at the time at which I am located. Knowing that I am present is no more ontologically significant than knowing that I am here. I cannot mistakenly hold either of these beliefs.