please help me with the following tense issue

Question

I am confused about which tense I should use in the following sentence

(a-1)To assess if heroin plays any role in causing depression, we first investigate if heroin users suffer episodes of depression
(b-1)To assess if heroin plays any role in causing depression, we first investigated if heroin users suffered episodes of depression

(c-1)To assess if heroin plays any role in causing depression, we first investigated if heroin users suffer episodes of depression

(a-2)To assess if heroin played ...

(b-2)To assess if heroin played ...

(c-2)To assess if heroin played ...

Can I make it all in the present tense IF the investigation has occurred ?

Can I mix the present tense with the past tense ?

Thanks

Fandorin · Accepted Answer

Hi Seraphin.
Can I make it all in the present tense IF the investigation has occurred ? You can use present tense in principle clause only if you're talking about main truths and facts, it's also called zero conditional
if ... present tense ...present tense.... "If you read a lot you reaches enough to work in huge company"
First conditional is used to talk about real possibilities in present and future or generally.
if ... present tense.... will...bare infinitive... "If you're working hard you will get good marks on your exams "
Sometimes you can use past tense in both parts of sentence in case you're talking about past but it's used rare.
(a-1)To assess if heroin plays any role in causing depression, we first will investigate if heroin users suffer episodes of depression. OK.

(b-1)To assess if heroin plays any role in causing depression, we first investigated if heroin users suffered episodes of depression. Wrong.

(c-1)To assess if heroin plays any role in causing depression, we first investigated if heroin users suffer episodes of depression. Wrong.

please help me with the following tense issue

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