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I wrote this sentence:

We suppose that two items are similar if they have been bought together by many people.

Should I say?

We suppose that two items are similar if they were bought together by many people

That sentence is the premise of a theory, it is a fact, not opinion.

item means product in this context

Marco Dinatsoli
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  • @Cardinal like we assume that two products are similar if many users bought them together. got me please ? – Marco Dinatsoli Aug 06 '16 at 21:31
  • @Cardinal that is a theory we are trying to check. the thing is not in the meaning of the sentence but in the grammar, don't worry about the truth (validity) of the sentence, that is what we are proving – Marco Dinatsoli Aug 06 '16 at 21:32
  • @Cardinal great, thanks man, is it clearer now ? – Marco Dinatsoli Aug 06 '16 at 21:38
  • that should be a face so it is always true, not just in the past or in the future, it is always true. but the buying action is in the past of course – Marco Dinatsoli Aug 06 '16 at 21:38
  • The only thing that comes to my mind is you would want to say something like this: "Two items are considered similar provided that many people buy them together" – Cardinal Aug 06 '16 at 21:53
  • similar in this context, doesn't mean similar by content, but "my similar" for example, people buy wine and cheese, so they are "similar" but less people buy "laptop and bread" together, (you don't get out of the store having laptop and bread) you got me guys ? – Marco Dinatsoli Aug 06 '16 at 21:53
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    @AlanCarmack I do not see any conditional sentences on that link. – Cardinal Aug 06 '16 at 22:03
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    @MarcoDinatsoli - Please read this link and decide whether you need to use the perfect here. Note the bolded advice: "Don't use the perfect unless you need it." Or try FumbleFingers's answer. Either one will help you. – P. E. Dant Reinstate Monica Aug 07 '16 at 01:11

1 Answers1

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We suppose that two items are similar if they were* bought together by many people.

You only 'suppose' if you have evidence to support a supposition. So when put together, these bolded statements make sense. 'If' is the modifier here. Your supposition only exists because of the word 'if.'

*You use 'were' in more affirmative statements. It it like subjunctive, but not quite - since English has no subjunctive, truly. It only has it in some cases. It is suitable for proving theory, since it implies you know that if products are bought together, they [then/therefore] are similar.

  • You use 'have been' in more present situations. If things are being bought right now, right here, in this moment, then it is appropriate to use 'have been.' It's a more hypothetical case. It means you only suppose your supposition if the following (buying products) has occurred. If it hasn't, then you don't suppose anything. You continue on supposing that they're dissimilar, until they are bought together.
user24986
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