A cousin of mine sent me an amusing email recently, and thankfully does not mind if I share it. She wrote: "I’ve always been confused on how to use empathize and sympathize in proper context."
Well, let me explain briefly! I know this can be confusing, and I've made mistakes about this point as well.
Sympathize: Much, much older word! It's been around since 1607, at the very least, when it was used in a dictionary to mean "to share the feelings of another."
Empathize: Empathize wasn't used to mean this until 1916, though it was used as early as 1865 it was used to describe “a physical property of the nervous system analogous to electrical capacitance, believed to be correlated with feeling.” A bit different, but an important difference to realize: they're not necessarily meant to mean the same thing! While that original definition did not last, the word morphed to mean “the ability to understand and appreciate another person’s feelings and experience.”
So, we have:
Empathize: “the ability to understand and appreciate another person’s feelings and experience.”
Sympathize: "to share the feelings of another."
Sympathize is appropriate in most contexts. Empathize is best suited to situations that you have experienced yourself, either in the real world or through the power of literature. Viola!