The machine generated an electric field where the N particles have an affinity for the M particles.

Can you use have instead of had when you're stating a scientific fact? I couldn't come up with a scientific fact in this example, so that's the best I could do, but let's assume the above is a true scientific fact. Is this grammatical or not?

  • I would say this is not grammatical, at least in a scientific paper, but in casual speech it would probably go by without comment.
    – randomhead
    May 16, 2021 at 5:11

2 Answers 2


Facts are usually expressed with the present tense:

A body in free-fall accelerates at 9.8 m/s²

But when you describe a particular experiment you would use the past tense:

The stone was dropped and accelerated at 9.8 m/s².

So you should decide if you are describing a general fact about the machine

The machine generates a field in which N particles have an affinity for M particles.

Or a particular run of the machine which occurred in the past:

The machine generated a field in which the N particles had an affinity for the M particles.

There is no rule against mixing tenses if you are talking about different times.

The baker made a cake which has pink icing and is in my cupboard now; we will eat it tomorrow.

Pythagoras wrote a theorem that the square of the hypotenuse of a right-triangle equals the sum of the squares of the shorter sides.


Facts are often stated in present tense just like news, for example: "Breaking News, Blue team defeats Red team by one goal". And when you get to it, you find out that the event took place hours ago.

I have seen such mix-ups, but I know there was a grammar for it. I had some friends who studied English translation and they told me that. I guess the text is wrong: either it is not the whole or it's just wrong.

  • This is an answer. If you want to comment to clarify a question you can do so. But this is not a comment. It is an attempt to answer.
    – James K
    May 16, 2021 at 7:46
  • @JamesK thank for... but i do not have the reputation to leave a comment would you PLEASE tell me how can I do it ???? I know its an answer I can read brother, but what can I do just look at my badge and see the number its 24 and I still have 26 reputation points to go for commenting... Please tell me what should I do ??? May 16, 2021 at 7:50
  • @JamesK thanks for editing though :) May 16, 2021 at 7:52
  • You get to comment at 50 reputation. Just write a couple of good answers or a couple of good questions. But don't use comments a space to write weak answers. Comments should be used to ask for clarification and to suggest improvements: not to write half answers.
    – James K
    May 16, 2021 at 8:33
  • @JamesK yeah You are right... but I have seen people answer in comments when they are not sure about their answers and i was not sure so I marked it as comment not an actual answer May 16, 2021 at 8:48

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