a- (Perfect)

The forms

• Maba — I have come (me + a-)
• Woaba — you have come
• Waba — he or she has come (ɔ + a-)
• Aba — it has come (ɛ- drops)
• Yɛaba — we have come
• Moaba — you all have come
• Wɔaba — they have come
• Kofi aba — Kofi has come

What it means
The perfect points to the result now: Kofi akɔ tells you Kofi is gone. That is why everyday questions use it: Woadidi? (Have you eaten?), Woate ase? (Have you understood?).

Perfect or past?
The simple past just reports an event: Kofi baa ha nnɛra (Kofi came here yesterday). The perfect says it matters now: Kofi aba (Kofi has come and is here). See Past or Perfect? and Simple Past Before an Object.

States and time
Some present states are said in the perfect: Mabrɛ (I am tired), Madi mfe aduonu (I am twenty years old). Clock time works the same way: Abɔ nnɔn nson (It is seven o'clock). See The Perfect for Present States, Talking About Age: di mfe and Telling the Time: abɔ nnɔn.

The negative
"Has not" does not use a-. It uses the negative nasal with a past-style ending: Kofi mmaeɛ (Kofi has not come). The a- turns up instead in the negative past: Mankɔ (I did not go). See Has Not: Negative Perfect and Did Not: a- + N-.

A look-alike
In a chain of verbs after a future, later verbs also take a-: Yɛbɛkɔ fie akɔdidi (We will go home and eat). That a- is not the perfect; see Consecutive a-.