Alexander, Samuel (1859-1938) Space, Time and Deity:
The Gifford Lectures at Glasgow, 1916-1918, Vol I.
Book II. The Categories.
Chapter II. Identity, Diversity, and Existence
...We have in fact noted already that either of the two, Space and Time, may be regarded as supplying the element of diversity to the element of identity supplied by the other. Any point-instant, or group of them, is therefore intrinsically itself, and other than some other, and indeed than every other, point-instant or group of them. It follows that existence is distinct from identity only in this reference or relation to the other. It therefore, to use another Platonic conception, "communicates" with the category of relation.
Book II. The Categories.
Chapter II. Identity, Diversity, and Existence
...We have in fact noted already that either of the two, Space and Time, may be regarded as supplying the element of diversity to the element of identity supplied by the other. Any point-instant, or group of them, is therefore intrinsically itself, and other than some other, and indeed than every other, point-instant or group of them. It follows that existence is distinct from identity only in this reference or relation to the other. It therefore, to use another Platonic conception, "communicates" with the category of relation.