For present purposes, Identity is the group of characteristics that makes one thing distinct from everything else. For example, the identity of “a” in “car” is something like the combined identities of:
1) the English letter A, 2) lowercase, 3) between the letters “c” and “r” in a three letter American English word for automobile, 4) written in this font and size. So, the above “a” is not c”A”r or c”a“r. But it is also not 5) c”a”t (different word), or 6) I love my c”a”r (combined with other words to form a different expression). Ok?
Now imagine the English Language Literati decide the letter C is confusing, redundant, and unnecessary (after all it merely combines the sounds of two existing letters: K and S). So they excise the excess. C is no longer recognized as a letter and S and K are substituted for C where it used to appear. What used to be spelled “car” is now “kar.”
Does this change the identity of the particular “a” referenced above? Of course – it’s no longer part of a (pardon the pun) real word.
Point being, the above “a” depends for its identity on many, many factors outside of itself. Things seemingly unrelated to that “a” – ie the abolition of the letter C – can greatly impact the very essence of that it is to be that particular “a.”
To a certain extent, this is true of all things – physical, psychological, simple, or complex. That is, the identity of one depends on traits of others that seem to be separate from and outside of itself.
For example, a circle requires a point from which all locations on the circle’s perimeter are equidistant. Where the point changes, so does the circle. 1+1=2 is only true within the context of certain numeral systems, eg true in base-10 but false in base-2 (binary). Color depends on light frequency and reflective/absorptive properties of material. Et cetera, et cetera.
Next, Part 2: Personal Identity