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The fossils preserved in the rock strata of the Grand Canyon have accumulated for a billion years and provide an invaluable geologic record.

I wonder why “provide” is not “provided”. I think “provide” has to be provided because there’s “and”. And the verb before “and” is “have provided”

I’ve been understood that a tense of the verb before “and” has to be the same tense as the verb after “and” Or it just has to be only the same type of speech not the same tense ?

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    It's not provided because they contuniue to do the "providing" of records today, in the present.
    – Tushar Raj
    Dec 23, 2018 at 8:35
  • I’ve been understood that a tense of the verb before “and” and a tense of the verb after “and” has to be the same. I’m sorry. I don’t understand it clearly
    – Kiw
    Dec 23, 2018 at 8:42
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    "I heard your question and will now try to answer it." See how the tense doesn't always have to be the same? And connects two clauses. They don't have to be in the same tense.
    – Tushar Raj
    Dec 23, 2018 at 8:48
  • Does it only have to be the same type ? Anyway thank you very much !
    – Kiw
    Dec 23, 2018 at 8:49
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    There is absolutely no rule of grammar that says anything about the tenses of the verbs on the two sides of a conjunction. Whoever told you there was is making things up (no doubt for the best of intentions, but I don't understand why). There are, obviously, often semantic restrictions. But if it makes sense to have different tenses, then we can do it.
    – Colin Fine
    Jan 22, 2019 at 19:12

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In grammar, parallelism, also known as parallel structure or parallel construction, is a balance within one or more sentences of similar phrases or clauses that have the same grammatical structure.The application of parallelism affects readability and may make texts easier to process. Wikipedia

But it might help to note that parallelism is just a stylistic recommendation to make your writing easier to read -- not using parallelism is not ungrammatical.

In your particular example, as far as tenses go the parallelism is kept intact.

The fossils preserved in the rock strata of the Grand Canyon have accumulated for a billion years and provide an invaluable geologic record.

Both verbs are in the present tense. 'Have accumulated' is present tense in the perfect aspect while 'provide' is present tense in the simple aspect.

There's a good article here which explains the differences between tense and aspect.

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I don’t think there are rules for this.

Tushnar Raj is correct. The invaluable geologic record continues to the present day. Its ongoing in the present until there comes a point in time that a condition changes it, which leads to the next example.

If I were to say, “…provided an invaluable geologic record”, then the geological record is no longer valuable in the present.

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