When vs. How Long

When and How Long ask for different things.

When usually asks for a specific point in time.

How long asks for duration of time, with a beginning to an end point.

When and how long often use different tenses and different verbs.

We can use the present perfect tense when talking about the connection of the present to the past. This tense is used to talk about actions that started in the past and is still ongoing and is most likely to continue in the future. For “how long” we usually use the present perfect tense.

There are “action” verbs that refer to actions or events that occur at a particular time, normally only once. In this context, these “action” verbs cannot be used with “how long” or expressing duration and should only be used with “when”. In this case, we use “status” verbs to show condition existing over a period time.

Examples:

Some common action/status pairs are as follows:

Using an “action” verb to indicate something that takes place over a period of time is a usual error.

Examples:

How long have you found out about his infidelity? X

How long have you known about his infidelity?

How long has she fell asleep? X

How long has she been sleeping?

How long have you bought the truck? X

How long have you had that truck?

Notice that all the statements above are using the present perfect tense which implies an ongoing occurrence. In the last sentence, it is talking about “still owning the truck”. Therefore, you have to use a “status” verb. In this case, instead of “buy” we use “have”.

( “Buy ” is an action verb therefore it cannot indicate something that has been happening over a period of time.)

We can also use “how long” to talk about events/situations that transpired completely in the past.

Examples:

Aside from length of time, “how long” can also be used to answer measured length of something.

Examples:

How long do you want your hair to be?

How long was the skirt she was wearing at the party?

How long is the bridge?