How does the present perfect progressive differ from the present perfect?

[Joe Carillo]

Question e-mailed to me by Farhad H. from Karaj, Iran (September 15, 2014):

I have a question:

What is the difference between the two sentences below?

(A) I have been thinking about writing Peter a letter.
(B) I have thought about writing Peter a letter.

Thank you. I look forward to your answers.

My reply to Farhad:

Sentence A, “I have been thinking about writing Peter a letter,” is in the present perfect progressive tense. It means that the speaker (the first-person “I”) started thinking about writing Peter a letter sometime in the recent past and continues to do so up to the present or the point of utterance. The action of thinking about the idea has not been completed and it’s possible—but not certain—that it may be continued beyond the point of utterance. Note that the present progressive tense is in the form = have + been + progressive (-“ing”) form of the verb.

In contrast, Sentence B, “I have thought about writing Peter a letter,” is in the present perfect tense. It means that the speaker (the first-person “I”) thought of writing Peter a letter sometime in the recent past until shortly before the point of utterance, at which time the action of thinking about the idea was completed or “perfected.” Note that the present perfect tense is in the form = have + past participle of the verb.

[Joe Carillo]

Follow-up question e-mailed by Farhad H. (September 15, 2014):

Do you mean that in the sentence "I have thought about writing Peter a letter," the speaker is no longer thinking about writing a letter to Peter?

My reply to Farhad H.:

Yes, in the sentence "I have thought about writing Peter a letter," the speaker is no longer thinking about writing a letter to Peter; very likely, he or she has abandoned the idea. Such a present perfect sentence is, in fact, usually followed by or is part of a statement that negates the idea, as in the sentence "I have thought about writing Peter a letter, but I changed my mind just now because I decided that he doesn't really deserve my apology for what happened."