Already Still Yet

These three TIME adverbs all refer to time before "now", up to "now". They are often used with the PERFECT or present form of the verb (simple or progressive).

1. Meanings

- Already = "sooner than expected".
- Still = "continuing later than expected".
- Yet = "before now" (yet is the form we usually use instead of already after negatives and in questions).

These three adverbs often express an element of surprise.

Examples:
(1) At a restaurant:
Mr. A: I've already finished my breakfast.
Mr. B: We haven't started yet.
Mr. C: We're still awaiting to give our order.

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(2) "I suppose you've already passed your driving test?" "No, I haven't even learned to drive properly yet. I'm still having lessons."

2. Already / still / yet with the PRESENT PERFECT

2.1. Referring to a past action with a present result

We use already, yet, and still with the PRESENT PERFECT to refer to a past action with a present result. Let's see examples below:
(1) "Is Cindy in her office?" "No, she's already gone home."
(2) "Do you know Mr. Jonh?" "Yes, we've already met."

2.2. Yet after negatives or in questions with the PRESENT PERFECT

We use yet after a negative or in questions with the PRESENT PERFECT. Let's see some examples below:
(1) "Sorry. I haven't done it yet. I'll do it in a minute."
(2) "Has Sam done his homework yet?" "No, he's started it, but he hasn't yet finished it.

Note: If we expect a "yes" answer to the question, we use already instead of yet.
Example: "Has Sam done his homework already?"

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2.3. Still before negative auxilliary hasn't / haven't + past participle

We use still before the negative auxilliary hasn't / haven't + past participle. Let's see example below:
(1) Sam still hasn't mended that table. He said he would mend it last week.

Notice that, in the sentences below, negative + yet and still + nagative have almost the same meaning, but example (2) emphasises the point and suggests that you are annoyed about it.
(1) I haven't passed my driving test yet.
(2) I still haven't passed my driving test.

Note (1): In U.S., the past simple is often preferred to the present perfect with already and yet.
Example:
(a) Have you already finished those letters? [G.B., U.S.]
(b) Did you already finish those letters? [U.S.]

Note (2): Already, still, and yet are also used with the past perfect.
Example: By the age of 20, John had already taken part in several national competitions. But he hadn't yet won any prizes.