1. I've recently read that oxygen might be poisonous

  2. I recently read that oxygen might be poisonous

It's a sentence I'd like to use in common conversation with a friend. Which one is correct grammatically and how to recognize that? I think the perfect would be better because I don't mean specified time and I don't give any details, but the past simple might be correct as well

Same question with

  1. I've thought this might be interesting. That's why I've brought it here.

  2. I thought this might be interesting. That's why I brought it here

  • 1
    Please do not imagine that a given conversation usage is "correct" or "incorrect", "grammatically" or otherwise. Why teachers do this to ESL students I will never understand. If you use the perfect instead of the simple past, no alarms will sound! You will enjoy yourself more, and learn more quickly and naturally, if you forget three quarters of what you've been taught about this or that usage being "grammatically correct" or not. Jul 24, 2017 at 23:47

1 Answer 1


Grammatically both of your first sentences are correct and idiomatic. One uses the present perfect, and the other uses the simple past. There's really no difference between them.

One might sound better than the other in the given context; for example if the other person used the present perfect to describe something, I might respond with a similar experience also using the present perfect.

A: I've heard that spinach is bad for you.
B: I don't know where you might have heard that, because I've recently read that it is good for you.

Your second pair of examples is a little different. With the verb "to think" the present perfect indicates a past complete or repeated thought.

I've thought about this a long time, and I believe we should paint the house red.

I've often thought the government was full of idiots, but after this latest news I'm sure of it.

If you want to express an ongoing and current thought, the present perfect progressive is idiomatic:

I've been thinking that it's time for our son to start sports.

I've been thinking that it's time I repay the favor you did me.

Unfortunately this is more about what is natural in English, rather than grammar rules. You might have to figure out what is idiomatic on a case-by-case basic, as a set of common expressions.

  • What about this example : 'You've really helped me by fixing my car' or 'You really helped me by fixing my car'. I know I would use the past simple one when reporting past events, but let's say my friend has just finished repairing my car. Would the present perfect sound good there? I'm not sure if it isn't describing circumstances of the "help". Jul 25, 2017 at 12:24
  • Yes, it's fine, although I think "You've been a big help by fixing my car" or "It's been a big help you fixing my car" is more idiomatic than "You've helped ..."
    – Andrew
    Jul 25, 2017 at 17:55
  • @JustAnotherPerson also please check my answer again, I made some edits to remove incomplete/incorrect advice.
    – Andrew
    Jul 25, 2017 at 18:37

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