Identity is not an object; it is a process with adresses for all the different directions and dimensions in which it moves, and so it cannot so easily be fixed with a single number. We know this in our own lives, for identity card, passport, birth certificate, social security number, driver's license, home address, bank account number, telephone listing, postal code, insurance policy number, national credit rating, all assign us an identity. The family dog might recognize us by pheromone, allelochemical or other trace odorant. We always reinforce our identity by washing, dressing, exercising, speaking, and interacting with others. In innumerable small ways we remind ourselves daily of who we are and to what we belong.
Lynn Margulis and Ricardo Guerrero: 'Two Plus Three Equal One, Individuals Emerge from Bacterial Communities'
The sailors mark him; more and more certain grow their suspicions of him, and at last, fully to test the truth, by referring the whole matter to high Heaven, they fall to casting lots, to see for whose cause this great tempest was upon them. The lot is Jonah's; that discovered, then how furiously they mob hime with their questions.
"What is thine occupation? Whence comest thou? What is thine country? What is thine tribe?"
Herman Melville: 'Moby Dick'
What has made the identity (persistence) of persons of special philosophical interest is partly its epistemological and partly its connections with moral and evaluative matters.
The crucial epistemological fact is that persons have, in memory, an access to their own past histories that is unlike the access they have to the histories of other things (including persons); when one remembers doing or experiencing something, one normally has no need to employ any criterion of identity in order to know that the subject of the remembered action or experience is (i.e., is identical with) oneself.
The moral and evaluative matters include moral responsibility (someone can be held responsible for a past action only if he or she is identical to the person who did it) and our concern for own survival and future well-being (since it seems, although this has been questioned, that what one wants in wanting to survive is that there should exist in the future someone who is identical to oneself).
Personal Identity. The Cambridge Dictionary of Philosophy