Becoming friendless is a harm, even if one does not know that one's last friend has just betrayed one. Likewise, one is harmed when the persons or causes one reasonably cares about are harmed, again whether or not one knows about the harm. But we also, I think, have the intuition that this is a different sort of harm from that which one undergoes when one loses an arm or when one is tortured. Call the first set of harms, extrinsic, and the well-being that they detract from extrinsic well-being, and call the second set of harms intrinsic. Apart from an incarnation, God is not subject to intrinsic harms, but he may be subject to extrinsic harms, such as when someone he loves (i.e., anyone at all) is harmed.
Now, introduce the intuitive notion of a temporally pure property. A temporally pure property is one that is had by x only in virtue of how x is at the given time. Thus, being circular is temporally pure but being married to a future president of the United States or being fifty years old are temporally impure. (If the fact that x has Fness is a soft fact, in the Ockhamist sense, then F is temporally impure.)
- (Premise) Only the having of an intrinsic property can constitute an intrinsic harm.
- (Premise) Ceasing to exist can be an intrinsic harm.
- (Premise) If presentism is true, only temporally pure properties can be intrinsic.
- (Premise) Ceasing to exist cannot be a property constituted in virtue of how x is at a particular time.
- Ceasing to exist cannot be constituted in virtue of one's temporally pure properties. (4 and definition)
- If presentism is true, ceasing to exist cannot be an intrinsic property. (3 and 5)
- If presentism is true, ceasing to exist cannot be an intrinsic harm. (1 and 6)
- Presentism is not true. (2 and 7)
This is of course in the same spirit as Epicurus' argument that death isn't bad because when you're dead, you don't exist and hence can't be badly off, and when you're not dead, you're not dead. But notice that Epicurus' argument fails to show that death isn't extrinsically bad. Also, I formulated the argument in terms of a (hypothetical) cessation of existence rather than death, since in fact death is not a cessation of existence for human beings, and it is not completely clear that death is an intrinsic harm to non-human animals.
Interestingly, the growing block theorist, who thinks only past and present events and things are real, has a similar problem. For if growing block is true, only hard properties (ones that depend only on how things were or are) can be intrinsic properties, and ceasing to exist is not a hard property.
The eternalist, however, can say that the property of being such that one ceases to exist is an intrinsic property, at least on one interpretation of "ceases to exist". It is an intrinsic property of oneself as a temporally extended being, the property of one's life being futureward finite. It is just as much an intrinsic property as the property of being circular or of finite girth. And if someone were to cause one to have the property of one's life being futureward finite, or a more specific property like that of one's life being being no more than 54 years long, she would thereby be imposing a harm on one.
And even the cessation of existence at age 54 as such isn't an intrinsic harm, the eternalist can talk of such intrinsic harms to someone as that one's life does not include any joys after the the age of 54, thereby doing some justice to the intuition that cessation of existence is intrinsically harmful.