Usamos as if para dizer como alguém ou alguma coisa se parece, se sente, etc.:
That house looks as if it is going to fall down.
Peter sounded as if he had a cold.
Peter is tired after the holiday. He doesn´t feel as if he has just had a holiday.
No nosso bom e velho Português corresponde ao "como se". That´s all folks...see you!