past tense & present perfect

English

past tense

One of the biggist areas of confusion for students is the difference between the past tense and the present perfect.

The past tense is indicated by use of the past tense marker, represented here by V(d). For regular verbs, the past tense form is indicated by the addition of an -ed at the end of the verbs. Here are some examples of regular verbs and their past tense forms:

However, some of the most common verbs in English are irregular. Altogether there are over 200 irregular verbs in normal use. Here are some examples:

Many people think that the past tense form only indicates past time. However, that is only one of the possible meanings. The past tense form is also use to express something that is unlikely or imaginary, from the speaker's point of view. Here is an example: "He wishes he had a car." The fact is that he doesn't have a car, so the use of "had" indicates that it isn't real: it's imaginary. "If he had a car, he could drive us to school." Again, "He doesn't have a car, so he can't drive us to school." This condition expresses something that isn't a fact. It's a conter-factual condition, which means it goes against what we know or believe.

Look at these two sentences:

If she waits another week, she can save money...

If she waited another week, she could save money because there's going to be a sale.

Both sentences are correct, but there is a difference in meaning. In the top sentence, the condition that she waits is more likely from the speaker's point of view. In the bottom sentence, the speaker thinks it's less likely that she's going to wait.

present perfect

When we talk about the experience or results, we use the present perfect form. This form uses "have" followed by the participle(分词).

For regular verbs, this participle is identical to the past tense form.

For irregular verbs, this participle is often different.

When we use the perfect form, the primary focus is on the subject of the sentense, not the verb. It emphasizes condition, experience or results rather than actions or events. In these two examples, we see the contrast. The top sentense gives the condition or state of the subject and the bottom sentense expresses an event.

She has already left the hotel.

She left the hotel a few minutes ago.

The top sentense describes the subject of the sentense, SHE, rather than an event. The fact that she has left the hotel is now part of her experience, or state of being. The bottom sentense expresses the action or event, "she left", which is something she did.

In general, the past tense form expresses events or act, and the prefect form expresses experience or conditions. When we use the prefect form of the verb, we focus on the state of the subject and not an action or event.

Note that the past form expresses events at specific points or periods of time, such as the last year or the past five years. These events are distanced from the speaker's point of view.

He worked at several companies. (in the past)
He finished the project last week. (in the past, last week)

The prefect form expresses the state of something from the speaker's point of view, not distanced in time.

He has worked at several companies. (his experience now)
He has finished the project. (his experience now)

These two sentenses are incorrect and confusing because they give two different point of view:

He has worked at that company until last week. (incorrect)
He has finished the project last week. (incorrect and confusing)

Here are some sentences that use the prefect form:

He has finished practicing.
He has been practicing.
She may have eaten.
Her computer may have been stolen.
He has practiced hard so he should do well in the competition.