What is the difference between "I learned to drive in 6 months" & "I learned to drive for 6 months"?

Question

I would say "I learned to drive in 6 months" emphasize how long it took to learn to drive & "I learned to drive for 6 months" emphasize how long it lasted and the continuity of the action.

Here are some of my studies:

In some dictionaries, they say

You use in to say how long something takes.

He learned to drive in six months.

The food was all eaten in a few minutes.

Be Careful!

Don't say that something lasts or continues 'in' a period of time. Say that it lasts or continues for that time.

I have known you for a long time.

I worked for the same company for ten years.

But in other dictionaries, they see "in" as "after a particular length of time" not "how long it takes"

in: after a particular length of time

to return in a few minutes/hours/days/months.

It will be ready in a week's time (= one week from now).

She learnt to drive in three weeks (= after three weeks she could drive).

But other dictionaries distinguish "in" when to say when something will happen & when to say how long someone takes to do something

We use in to say how long it takes someone to do something:

He was such a clever musician. He could learn a song in about five minutes.

We use an apostrophe -s construction (in a year’s time, in two months’ time) to say when something will happen. We don’t use it to say how long someone takes to do something:

I won’t say goodbye because we’ll be seeing each other again in three days’ time. We can also say in three days, without time, in this example.

He ran the marathon in six hours and 20 minutes.

Answer 1

1. I learned to drive in six months

It took the speaker six months to learn "how" to drive.
Result: Today, the speaker knows how to drive, and I would understand that he or she passed their driver's test.

2. I learned to drive for six months

At a specific moment in the past, someone taught the speaker how to drive for six months but for an undisclosed reason, the speaker either stopped learning or stopped driving.
Result: The sentence implies that the speaker does not drive today or stopped learning to drive.

Answer 2

The problem with "I learned to drive for 6 months" is that it's likely to be parsed as "I learned to (drive for 6 months)" rather than "I (learned to drive) for 6 months". It would be more natural to use different wording, such as "I took driving lessons for six months."

Answer 3

• I learned to drive in 6 months.
• ** I learned to drive for 6 months.
• ** I was learning to drive in 6 months.
• I was learning to drive for 6 months.
• ** I practiced driving in 6 months.
• I practiced driving for 6 months.

I put **s by the invalid sentences above. Now an explanation:

With "I learned to drive in 6 months" the "in 6 month" indicates a point in time (somewhere in 6 months). With "I learned to drive for 6 months the "for 6 months" indicates an interval of time.

The act of learning to drive has duration followed by a change of state. "I learned to drive" is talking about the change of state, so its compatible with a point of time (in 6 months) but not an interval (for 6 months).

You could change things to not involve a change of state so it works with an interval by using the past progressive form (which then indicates the learning may not have completed).

• I was learning to drive for 6 months.

Note that "I was learning to drive in 6 months." is wrong, the state change that would fit the point in time is no longer available to fit the "in 6 months"

You could also choose an action that doesn't involve a state change by using practice instead of learn. With that change its compatible with the interval, but not the point in time.