'Is influenced' - Helping verb and main verb in different tenses

Question

I have learnt that both helping and main verb should be in the same tenses.

For example: The design of ABC was influenced by DEF. In the above sentence, since the main verb influenced is in past tense, the helping verb was is appropriate.

However, I have seen the following sentences, where the tenses of both helping verb and the main verb do not match.

For example:

1. The design of ABC is influenced by DEF
2. He is scared by many incidents.

Both in examples 1 and 2, the tense of helping verb is doesn't match with the tense of main verb.

Is this wrong or acceptable? Please explain.

Answer 1

1. It is raining.
2. It was raining.
3. She has gone.
4. She had gone.
5. They are influenced.
6. They were influenced.
7. They can leave.
8. They could leave.

Another term for "helping verbs" is "auxiliary verbs".

In each sentence in (1-8) we can see an auxiliary verb and a main verb. In English only the first auxiliary can have any tense. In the sentences above we can see that in (1,3,5,7) the auxiliaries are in the present tense. In sentences (2,4,6,8) they are in the past tense.

The verbs after the auxiliaries never have any tense. In English we have three verb forms that have no tense. There are two participles: the -ing form and the 3rd form. There is also the plain form.

We use the -ing form in continuous constructions such as (1,2). Notice that only the auxiliary changes when we go from present tense to past tense. We can use a past or present tense auxiliary with the same participle, raining.

We use the 3rd form in perfect constructions such as the present perfect or past perfect as shown in sentences (2, 3). Again notice that only the auxiliary verb changes when we go from present tense to past tense. We can use a past or present tense auxiliary with the same participle gone. Notice that for many irregular verbs the 3rd form is different from the past tense form. The past tense of GO is went not gone.

We also use the 3rd form in passive constructions as shown in sentences (4, 5). Again notice that the only the auxiliary changes when we go from present tense to past tense. We can use a past or present tense auxiliary with the same participle, influenced. Notice that even though the past tense form of many verbs looks the same as the 3rd form, we only see the third form after auxiliary verbs. Here we see the 3rd form of INFLUENCE, not the past tense!

In sentences (7,8) we see past and present forms of the modal auxiliary verb CAN. Notice that we always use a plain form after modal verbs. It doesn't matter what tense the modal verb is in.

Conclusion

When we have auxiliary verbs or 'helper verbs', only the first auxiliary verb in the verb phrase has tense. All the verbs afterwards are always participles or plain forms. Participles and plain forms have no tense. In English the 3rd form and the past form often look the same. But the verbs we see after an auxiliary are never past tense. Therefore, both of the Original Poster's sentences are perfectly grammatical.

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Grammar notes:

Some grammars and EFL course books call the -ing form the 'present participle' and the 3rd form the past participle. These are stupid names for these words. These words have no tense. We can use the past participle in present tense sentences and the present participle in past tense sentences. The grammarians who gave these words these stupid names died a long time ago, so we don't need to be angry with them any more.

According to some grammars, modal verbs don't have tenses. However, most grammarians agree that they do.