Still, already and yet

Still
Usamos still para dizer que uma situação ou ação está em andamento.
Exemplos
  • It’s 11 o’clock and Pedro is still in bed.
  • When I went to bed, Maria was still working.
  • Do you still want to go to the party or have you changed your mind?
 
Still geralmente vem no meio da frase com o verbo.

Yet

Yet = “até agora”. Usamos yet principalmente nas frases negativas (I haven’t finished yet) e perguntas (Have you finished yet?). Yet mostra que o falante está esperando que algo aconteça. Yet normalmente vem no final da frase.
 
Exemplos
·         It’s 10 o’clock and Pedro hasn’t got up yet!
·         I’m hungry. Is dinner ready yet?
·         We don’t know where we’re going for our holidays yet.
We often use yet with the present perfect (Have you finished yet?).
Compare yet and still:
  • Pedro lost his job a year ago and is still unemployed.
  • Jack lost his job a year ago and hasn’t found another job yet.
  • Is it still raining?
  • Has it stopped raining yet?
Still também pode vir em frases negativas (antes da particula negativa):
Exemplo
  • She said she would be here an hour ago and she still hasn’t come.

Already

Usamos already para dizer que algo aconteceu antes do esperado. Normalmente vem no meio da frase.
Exemplos
  • When is Sue going on holiday? She has already gone! (Sooner than you expected)
  • Should I tell Liz the news or does she already know?
  • I’ve just had lunch and I’m already hungry.

Referências bibliográficas
English Grammar in Use – Cambridge University Press