I have seen a plane.
Here, what is the meaning of the sentence above? I understand the basic meaning of 'have pp'. The sentence above means that I have just seen a plane? Or I have seen a plane before? Or both according to the context?
I have seen a plane.
Here, what is the meaning of the sentence above? I understand the basic meaning of 'have pp'. The sentence above means that I have just seen a plane? Or I have seen a plane before? Or both according to the context?
A lot of the meaning comes from context - what this is in response to.
In isolation it seems a strange thing to say unprovoked, and might get a response of 'Well, who hasn't?'.
If it is in response to 'What have you seen through the window?' then it has your first meaning - 'just seen'. If it's in response to 'Hey- that's a plane! Did you know that?' then depending on intonation and emphasis it could be a sarcastic or patient reply in your second sense.
So yes, it could mean either depending on context.