Present Perfect with 'for' + time period

Question

#1

I have known this for 2 days.

The above sentence means

• "I got to know this 2 days ago" and/or "2 days have passed since I got known this".

Right? That looks and sounds clear to me.

#2 Another sentence:

I have lived in London for 2 years.

Let's assume that some time ago I lived in London, but now I live in a different city. Taking that into an account, which is the correct meaning below?

1. (similar to example #1) "I started to live in London (for the first time) 2 years ago and now it has been 2 years since I started to live in London (for the first time)."
2. (unlike the meaning of example #1) "The total amount of time I lived in London is 2 years."

It looks like (2) is correct here.

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Above, I gave you 2 examples which have different meanings though they have the same grammar form. In those cases it was obvious to me which meaning was correct.

But how about this example?

#3

I have played this computer game for 3 years (I started playing it in the past and I finished playing it in the past).

1. Is it (similar to example #1)
   "3 years have passed since I played the game for the first time, until now" ?
2. Or is it (similar to example #2)
   "3 years have passed since I started playing the game, until I finished playing it" ?

If (3.1) is correct, then how to change the sentence so it has the (3.2) meaning?
Otherwise, if (3.2) is correct, then how to change the sentence so it has the (3.1) meaning?

Answer 1

The Universal and the Existential senses of the Present Perfect construction, as described by McCawley, occur with different kinds of predicate.

Stative predicates like be blue or own a house are one thing -- states start, continue, and end, but they tend not to repeat.

• (a) The Universal sense of the Perfect is used to indicate that a state of affairs (with a stative predicate) prevailed throughout some interval stretching from the past into the present
  • I've known Max since 1960.

Active predicates (not to be confused with the "active voice" that supposedly opposes the Passive construction) like run a mile or rent a house, on the other hand , typically describe motion, human agency, and intermittent or short-term phenomena.

• (b) The Existential sense of the Perfect, used to indicate the existence of past events (with active predicates), during some interval stretching from the past to the present
  • I have read Mrs. Galloway five times since it was published.

As for the preposition, for is used to indicate the duration of states, and of time periods determined by actions:

• He's been at college for 3 years now.

• He's been studying medicine for 3 years now.

• He's studied medicine for 3 years now.

• He studied medicine for 3 years.

• She ran marathons for 14 years.

• *She ran a marathon for 14 years

Note that She ran marathons is a generic sentence; it classifies her as a marathon runner, but no specific event is referred to. If it's a specific event, its duration doesn't occur with for, unless it refers to actual event duration.

Answer 2

If you want to say that at some time in the past you lived in London for two years, use the simple past, since the present perfect could be understood to mean that you have been living there for the last two years:

I lived in London for two years.

If you lived in London twenty years ago for two years, the following is actually not a simple sentence despite what the inadequate punctuation might suggest.

I have lived in London for two years.

What you have actually said is as follows:

I have lived in London -- for two years.

There are two assertions there, and two separate independent clauses, the latter with ellipsis:

I have (indeed) lived in London -- [and I lived in London] for two years.