Saturday, June 2, 2018

Acting without existing (any more)

Thesis: It is possible for an object to be acting while it does not exist.


Imagine a rattlesnake that is ten light-years long, all stretched out. For all one hundred years of life it has been deliberately rattling its rattle. And then at the end of its hundred years, its head is destroyed, and I assume that the destruction of the head of a snake is sufficient for its death.

Rattling continues for at least about ten years even after the snake is dead, since the nerve signals the brain had sent while the snake was alive are continuing to rattle.

If this post-mortem rattle counts as the snake’s activity, the Thesis is established. But it is not clear that this ten years of post-mortem rattle is the snake’s activity.

But now consider the last year of pre-mortem rattling, call it R99 (since it starts in year 99 of the snake’s life). Whatever one says of the post-mortem rattling, clearly R99 is the snake’s activity. However, there is a reference frame—the way I set the length of the snake and the times in the story guarantees this—in which R99 occurs after the snake’s head has been destroyed, and hence occurs after the death of the snake. But R99 is the snake’s activity. Hence, there is a reference frame where an activity of the snake occurs after the snake is dead.


Obviously, only existent things can act. But while existence simpliciter is important for activity, existence-at-a-time does not have the same kind of significance. Obviously, often an actor’s action has a relationship R to some thing x that the actor itself does not have. For instance, an agent’s action may be known by me without the agent being known by me (here, R is being known and x is me).

Now, when we say that Elizabeth II exists as Queen of Canada, that is just an awkward way of saying that she has a monarchic relationship to Canada, rather than being a claim about that mysterious thing deep ontology studies: existence. I think we should think of existing-at-a-time as not really existence but simply as a particular kind of relationship—an occupation or presence relationship. It is not surprising in general that activities can stand in relationships that the agents do not. So, why can’t an activity stand in an occupation relationship to a time that the agent does not?

I think much confusion in philosophy comes from thinking of existence-at-a-time and existence-in-a-place as something special, somehow deeply ontologically different from other relations.


James Goetz said...

Hi Dr Pruss,

I suppose your snake analogy has more to do with the fuzzy definition of *death* for a reptile than your view of relational identity. For example, the body of a decapitated snake can continue to move hours. For instance, here is a video of a decapitated snake that bit its own twitching body (, while this video has made various rounds in social media and was commented on in a NATIONAL GEOGRAPHIC blog (

Also, the definition of *death* for a human is fuzzy because CPR sometimes restores life to a human corpse in the stages of pallor mortis or algor mortis.

Alexander R Pruss said...

You can run exactly the same story for a really tall human. I think we are agreed that total destruction of the head kills a human.

I also think that the possibility of a decapitated body moving around does not imply that the body is alive.

Walter Van den Acker said...


A decaptitated body moving around doesn't imply that the body is alive but it does imply that the body exists, so it is not an example of something that acts while it doesn't exist anymore.
Actually, I don't think there are any exmaples of something that acts while not existing anymore. In the case of the snake, the muscles that are responsible for the rattling still exist and so does the signal from the snake's brain. We still receive light from stars that vanished thousands of years ago, but the light of the star still exists, so it is the remaining existing part of the non-existing thing that is actually responsisble for the action.

Alexander R Pruss said...

Yes, but the point is that in my relativistic snake's tail wiggling, the wiggling is an activity of the snake, as can be seen by considering a reference frame where the snake's head is still in place when this wiggling event happens.

James Goetz said...

I am still trying to understand your thought experiment. Are you assuming that relativity and the length of the snake make the snake dead and alive at the same time?

I doubt that.

First, a *reference frame* consists of an abstract spacetime coordinate system and the set of physical reference points that align the coordinate system and standardized measurements. And an *inertial reference frame* is a reference frame with zero or constant velocity.

Second, the relativity of simultaneity implies that two events are causally disconnected when the time interval between them is less than the spatial interval between them divided by the speed of light; while no two causally disconnected events are absolutely simultaneous to each other.

I think you are trying to imply that the relativity of simultaneity implies that the ten light-year long snake has a causal disconnection between its brain and parts of its body. Is that correct or do I misunderstand you?

Assuming that the nervous signal sent by the snake brain travels the speed of light, then that signal and the consequences of it are never causally disconnected from the snake brain. However, nervous system signal travel in the order of 100 meters per second, which is much slower than the speed of light. In any case, I see no causal disconnection and relativity of simultaneity in this thought experiment. Or am I missing something?

Walter Van den Acker said...


The snake's head being in place or not makes no difference because at the time the tail wiggles, the signal has already left the snake's brain and has arrived at the tail.
The existence or non-existence of the head is not important, the only thing that matters for the wiggling is the existence of the signal, the muscles and the tail.
Unless you want to apply relativistic effects that make events simulataneous, but in that case, there is a reference frame in which the snake's head is still in place when the tail wiggles.
I don't think it makes any sense to say that something that doesn't exist anymore can act.