Ursula K. Le Guin discussing her regrets about not using more gender-neutral language in her book 'The Left Hand of Darkness', the significance of pronouns, and the grammatical accuracy of the singular 'they':
"English has a truly ungendered pronoun only in the plural. He, she, and it are gendered, they is not. [...] Historically, and colloquially, they has been regularly used as an ungendered or bisexual singular."