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I have the following idea, The first part is written in a present form as it is more general. As I explained what I did in the second part, it is written in past tense. here is my example.

  1. The proposed graph analysis method is based on a correct segmentation of point data.
  2. The work in this study mainly focused on the modeling process.

And I join them using and as follows.

The proposed graph analysis method is based on a correct segmentation of point data and the work mainly focused on the modeling process.

Now, I am doubted whether we can keep two tenses within a one single sentence. Any idea please.

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    They are not in a different tense; the second is is implied: The ... method is based on ... and the work [is] mainly focused on....
    – choster
    Oct 23, 2013 at 20:15
  • @gnp choster is reading your sentence as an (unintended) example of gapping.
    – user230
    Oct 23, 2013 at 20:34
  • @choster There is no such elision of "is" possible; if that is the intent, it is not grammatical. By removing "is" from "is focused", you end up with "focused", which unambiguously becomes the verb of the sentence, since no other verb is visible.
    – Kaz
    Oct 25, 2013 at 19:45

3 Answers 3

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The problem here is that you are using coordination: [present clause] AND [past clause]. Joining sentences from different times in this way is somewhat awkward.

Changing tense is smoother if you subordinate the second clause to the first:

For instance, if a causal relationship applies:

The proposed graph analysis method is based on a correct segmentation of point data, because the work in this study mainly focused on the modeling process.

In any case, there is no reason why the past tense cannot be brought into the present. We can speak about studies in the present tense:

The study mainly focuses on the modeling process.

This point of view can be used even if the study concluded years ago. The present tense does not imply that the study is still going on. If that were the case, this imperfective situation would be expressed with a gerund like this:

The study is mainly focusing on the modeling process.

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Since they're both independent clauses, you can join them in this way, but without a comma before the "and" that joins them, it becomes a run-on sentence (and may be misinterpreted, as choster mentions in the comments):

The proposed graph analysis method is based on a correct segmentation of point data, and the work mainly focused on the modeling process.

A simpler example of joining two independent clauses of different tenses would be something like this:

I'm going to the store today, and my mother went yesterday.

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  • thanks but in your example both are past tense I guess. not present and past.
    – gnp
    Oct 24, 2013 at 8:47
  • With the comma, they can also be misinterpreted in the exact same way. But since the misinterpretation means almost the same thing as the original, that doesn't really matter. Oct 24, 2013 at 18:52
  • @gnp D'oh! You're right. Corrected example sentence.
    – Haywain
    Oct 25, 2013 at 19:02
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I think Kaz's answer is a good one. As Kaz says, we can speak about studies in both the past and the present tense. One way to think of this is that the study was done (in the past), but it is also available in the present.

Kaz assumed that there is a causal relationship between the two sentences, and if this is true, then it makes sense to use "because," as Kaz suggests. But if there is no causal relationship involved, it would be better to write this in two sentences, exactly as you wrote them in your example:

"The proposed graph analysis method is based on a correct segmentation of point data. The work in this study mainly focused on the modeling process."

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