You can spot an Irishman or a Yorkshireman by his brogue. I can place any man within six miles. I can place him within two miles in London. Sometimes within two streets.

Higgins says these lines in Act 1 after Pickering asks him how he is able to detect the pedestrians' places of origin after merely hearing them speak. Right from the beginning of the play, the importance of language in relation to one’s identity is highlighted. Higgins’ almost supernatural ability to place a person based on their manner of speaking is introduced, as is the high regard he has for language.

No, sir: you’re not at all particular when you’ve mislaid anything or when you get a little impatient. Now it doesn’t matter before me: I’m used to it. But you really must not swear before the girl.

In Act 2, Mrs. Pearce warns Higgins to be wary of the language he uses in front of Eliza. For all of Higgins’ emphasis on the importance of language and speaking well, Mrs. Pearce reveals that at times Higgins uses language that isn’t suitable for a gentleman. So while Higgins understands language at the scholarly level, Mrs. Pearce is aware of the language of manners. For Eliza to truly succeed as a lady, she will have to learn both.

Last night, when I was wandering about, a girl spoke to me; and I tried to get back into the old way with her; but it was no use. You told me, you know, that when a child is brought to a foreign country, it picks up the language in a few weeks, and forgets its own. Well, I am a child in your country. I have forgotten my own language, and can speak nothing but yours.

In Act 5, Eliza rejects Higgins’s suggestion that she return to where she came from.  She knows that with her newfound ability to speak "properly,” as a lady would, she cannot fit back into her own life. Language and identity are inextricably tied, and, as Eliza suggests, to give up one’s own language is to give up one’s identity and past. Higgins has left Eliza in a difficult position , where she is not quite a “true” lady but can never return to being just a flower girl.