The one thing you need to know for a good life: A is A.

Aristotle’s famous law of identity states that “A is A” — that is, a thing is identical to itself. While this may seem fairly trivial, it’s actually pretty profound in a couple of fundamental ways:

• Once identity is established (that is, we confirm that two things are identical), then all the attributes of that thing are also attributes of the other, identical thing and may even share attributes with things that are similar in important respects (this particular copy of Hemingway’s For Whom the Bell Tolls is identical to itself, but it shares many important attributes with other copies of the novel, most critically the text, for example).
• Everything has its own unique nature, and even though many attributes may be shared with similar things, that one thing is identical only to itself — if something else shares exactly all the attributes of that thing, then they are by definition the same thing, not two different things. For us humans, it means we are unique and have our own specific nature: even though we share many attributes with other humans, each one of us is identical only to ourselves and therefore unique.

The 18th century Irish philosopher, Bishop Berkeley, stated it a little more exclusively: “a thing is what it is, and no other thing.” For my purpose here in talking about us humans, each one of is what we are — and not…