Over at The Toast, a clear and excellent explanation of why English pronouns are the screwed-up and confusing things that they are, and why grammatical gender isn’t the same as actual real-people-doing-real-things gender, and how we got the confusing mess we have today:
A sample (on the subject of how third person singular “they” fell into grammatical disrepute despite a long history of pre-existing usage):
But then, in the late 18th century, grammarians started recommending that people use he as a gender nonspecific pronoun because they was ostensibly plural, as part of the grand tradition of awkwardly shoehorning English grammar into Latin which has caused many of your present grammatical insecurities, and which I’m totally sure had nothing whatsoever to do with the patriarchy.
The rest of it is just as good. Go, read, have fun.
Dr. Doyle's Blog 