How to understand the use of "used to"?

Question

I have talked about these two verbs "used to" and "might" with my tutor. She told me that we can use them when we want to show that some activity was done many times in the past. She also told me to remember that we don't use those two verbs with definite time expressions. She told me that it isn"t grammatically wrong but just unidiomatic. I forgot to ask one more question so I'm gonna ask you.

1. In the past, I used to drive a truck for 7 years in that firm

2. In the past, I might drive a truck for 7 years in that firm

As I understand my examples aren't natural, but what if I said something like that by mistake ( I mean what if I add a definite time expression to those two verbs). Would you understand that 1 and 2 mean that during a single seven year period I sometimes did something or that I did something here driving a truck many times in the past and each attempt took seven years?

Answer 1

Constructions like used to [bare verb] (e.g.used to go, used to sing) refer to actions in the past that happened regularly or to a situation that was ongoing, such as a job.

When I was a kid, we used to go to the beach every summer.

When I was in college, the entire student body used to pack the campus theater on Friday night to watch a movie together on the big screen.

She used to be a ballerina but suffered an injury to her leg and could no longer dance.

When might is used to refer to past actions, it refers to actions that were usual yet unusual, not unusual yet in some way unusual, somewhat out of the ordinary but not completely so, something which happened more often than occasionally:

When I was an intern at that company, I would go for weeks with almost nothing to do and then a project would come along where I might have to work overtime for a month straight.

When we were kids, we didn't have video games. After dinner, and after our homework was done, we used to go outdoors at dusk and play hide-and-seek or flashlight tag when it got dark. Or we might throw stones up at bats to make them think it was an insect.

And so we could rewrite the sentence about watching movies in college:

When I was in college, the entire student body might pack the campus theater on a Friday night to watch a movie together on the big screen.

If it didn't happen every Friday night, but happened often enough to be considered a fairly regular thing, you could use might instead of used to. It was not unusual for us and yet in some sense it was unusual.

Answer 2

The short answer to your specific question is that context will often lead a listener to correctly understand your meaning. For example, consider your first sentence:

In the past, I used to drive a truck for 7 years in that firm.

What you're really asking is, What does for seven years refer to? Now it's theoretically possible that you are describing a job where you had shifts requiring you to drive continuously for seven years. But any good listener will understand immediately the common sense meaning: You worked for the company for seven years, and during that time you regularly drove trucks.

Having said that, my advice is that if you have any doubts about your meaning, try to rewrite or rethink the whole sentence. In both writing and speaking, one good way to do that is to simplify and shorten your language units. For example:

I worked in that firm for seven years. During that time, I used to drive trucks.

I worked in that firm for seven years. My main job was in the store room, but I might drive trucks as well if the main driver was on leave.

Note that in this case used to implies regular activity, whereas might implies occasional and less frequent activity.