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I am confused on whether to use past tense or present tense in the same sentence that has present perfect tense.

For example,

1) I have looked at the plot but did not see anything wrong with it.

This seems wrong grammatically as have is in present tense while did not is in past tense. However, it makes sense from another perspective because I have looked at the plot (meaning the action of looking is already in the past) thus using did not does make sense.

2) I have looked at the plot but do not see anything wrong with it.

This should be grammatically correct but does this alter the meaning of sentense (1) (assuming (1) is correct)?

3) I looked at the plot but did not see anything wrong with it.

I am quite certain that (3) is correct but sometimes I would prefer to use it in present tense (using have/has).

My analysis might be totally off but please bear with me and show me the right direction.

Thanks!
Comments  
I looked at the plot.(In the past)

I have looked at the plot. ( I am aware of the situation now. I have knowledge of the situation now.)

I did not see anything wrong with it. (In the past)

I haven't seen anything wrong with it.(Up to now it seems to be OK)

I don't see anything wrong with it. (Now)

These are all correct and can be used in any combination.

The simple past is referring to the completed past action and the present perfect is referring to a present condition or result of a past action.
Nice separation, myprofe.
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When you say any combination is correct, does that include:

1) I looked at the plot and don't see anything wrong with it.

This sounds rather weird as it means I looked at it in the past (let say a year ago) and see it now.

It would be even weird, in fact ridiculous, if the sentence is:

2) I look at the plot and didn't see anything wrong with it.

Meaning I look at it now and 'see' it in the past. I know this is not part of my original sentences.

Really appreciate your response. Please clarify this, thank you.
New2grammar
1) I have looked at the plot but did not see anything wrong with it.

2) I have looked at the plot but do not see anything wrong with it.

3) I looked at the plot but did not see anything wrong with it.

I would say:

- I have looked at the plot but have not seen anything wrong with it. (= The speaker is currently in the opinion that there is nothing wrong with the plot. )

- I looked at the plot but did not see anything wrong with it. (= this has nothing to do with "now". The speaker is talking about a specific past event as if to answer a question like: "What happened then?")

- I am looking at the plot but do not / cannot see anything wrong with it. (now)
Anonymous
When you say any combination is correct, does that include:

1) I looked at the plot and don't see anything wrong with it.

This sounds rather weird as it means I looked at it in the past (let's say a year ago) and see it now.

You looked at the plot in the past but your opinion, even though it was first made in the past, is still valid now.

I saw the film and I liked it. I saw/have seen the film and I like it. I liked it then and I still like it now.
Anonymous thenIt would be even weird, in fact ridiculous, if the sentence is:

2) I look at the plot and didn't see anything wrong with it.

No, this sentence doesn't make any sense. In the other examples we were using the past simple or present perfect in the first clause and the past simple or present simple in the second clause.

I saw Mary the other day. She looked well.

I saw/have seen Mary. She looks well.

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Thanks!! It's much clearer to me now
1) I have looked at the plot but did not see anything wrong with it.
"I have looked" is Present Perfect (present aux + past participle); this combination implies present but points to the past. You could also you "I looked" but this would be simple past (see #3). However, You should not use "but" at all because this word is use when comparing clauses (I'm sad, but I'm smiling.); here you are not comparing anything. "did not" does sound a bit awkward. I would say this:
"I've looked at the plot and see nothing wrong with it."

2) I have looked at the plot but do not see anything wrong with it.
If you want to say "do not see", you can say:
"I've looked at the plot and do not see anyting wrong with it." -- no "but", use "and" to combine the two clauses.

3) I looked at the plot but did not see anything wrong with it.
Here you are using simple past "I looked"; you should probably use simple past to follow it up:

"I looked at the plot and saw nothing wrong with it", or, "I looked at the plot and saw not a thing wrong with it."

I hope this helps,
-Andrew