I saw a dog.

I have seen a dog.

What are the differences between them?
Did these events happen on the same day?

  • They could have happened 5 minutes ago, or they could have happened 5 weeks ago. All we know is it's happened in the past.
    – J.R.
    Dec 14, 2014 at 4:14
  • 5
    I just tried to explain why it's hard to give a fully satisfactory to this question here.
    – Ben Kovitz
    Dec 14, 2014 at 4:16

7 Answers 7


Sometimes they can mean the same thing, especially in US varieties of English. Sometimes we would use the first (simple past) when the consequences or result of the act of seeing are not particularly relevant to a current situation, and the second (present perfect) when such a connection is in operation.

There are many other factors, some very nuanced and subtle, which may determine if we must or would tend to use one over the other.

As with English grammar generally, the simple, more basic rules are worth learning, but we will best learn to make the correct choices more and more often by immersing ourselves in the language rather than trying to memorize myriad complex rules, and then retreive and use them while producing language--an impossible and endlessly frustrating undertaking.

  • 1
    I think memorize was a much clearer word. The important thing is to discourage people from trying to learn the difference by memorizing hundreds of piddly rules for specific situations.
    – Ben Kovitz
    Dec 14, 2014 at 6:34
  • Memorize is still there, just not repeated. I think memorize includes storing, or certainly can, so wasn't logical in the list of acts. Yes. It's like learning to ride a bicycle by reading sets of instructions. It doesn't help people, but our beliefs in this area tend to transcend the rational. Dec 14, 2014 at 6:43
  • Ah, I hadn't noticed the preceding memorize. I'm a little worried that "encode" is too obscure an idea for a typical EFL learner, though.
    – Ben Kovitz
    Dec 14, 2014 at 6:46
  • How about "recall" to replace the whole computer-storage-and-retrieval metaphor?
    – Ben Kovitz
    Dec 14, 2014 at 6:48
  • It's language that brain and learning scientists use for cognitive processes. Maybe the computer is the metaphor, then. :) But it will be better to make the whole point more simply. Dec 14, 2014 at 6:57

In the past I saw a dog.

Now I have seen a dog.

The difference is the time period you are talking about. The Simple Past saw is used to talk about past events while the Present Perfect have seen is used to talk about things that are true now, in the present. They are semantically different but logically equivalent. Since you saw a dog in the past it must be true that you have (ever) seen a dog now.

The past could be earlier today or further back. It could be the same dog and occasion you are talking about in both sentences or it could be two different dogs, or even the same dog on different occasions. I just saw a black dog but I have seen a white dog before.

  • This is flat-out wrong. Both tenses are most often used to talk about past events. The most important difference between them involves how they are conceptualized from the viewpoint of the present. Dec 19, 2014 at 16:06
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    @JimReynolds I believe that is exactly the point I was making
    – CJ Dennis
    Dec 20, 2014 at 1:17

I saw a dog.
I have seen a dog.

Both talk about the past event but, the former one is more about a one-off event whereas the second talks about the event whose impact still lies. A very subtle difference if you could see.

I saw a dog - one time event in the past -today, yesterday...does not matter

But in the context of have seen, you need to have the effect to be continued at least till the time you speak the sentence

I have seen a dog with two tails -day does not matter.

The thing could be usual or unusual but the effect still remains.

Though I live in India, I'm lucky to have seen penguins! Here, I won't use saw because though it was a one-time event, the effect still remains...

I have seen penguins. They were in Toronto Zoo.

The moment I shift from have seen to saw, it becomes a one time event and the impact may lack.

I saw penguins in Toronto Zoo ~ Okay, what next?

This is the reason, we often use have you seen when we want to keep the effects intact over did you see being a one-time event in such context.

Not sticking to strict grammar rules, if you ponder over this topic you'll find that whenever we use have seen/done or whatever the effect will remain till you speak that. The flair of suspense, surprise, information or the like still remains over the use of saw/did etc.

  • It has to do with the time the event took place and if it continues into the present. If you told your friends about your trip to Toronto and said ' I saw penguins at the zoo in Toronto' it would be right. If you said ' I have seen penguins at the zoo in Toronto' it wouldn't be right because the listener would wait for you to give additional information. If you visited a different zoo and saw penguins you would say 'I have seen penguins at the zoo in Toronto and they were much bigger than the ones they have here'.
    – Chris
    Nov 23, 2016 at 19:36
  • Many people would still use the simple past in this context because it's just simpler and easier. It gets tricky if you want to assign a specific or unspecific time period. An unspecific time could be ' in the last year' while 'the last year' could be a specific time. So you would say ' I saw penguins at the Zoo in Toronto last year' and ' I've seen penguins at the Zoo in Toronto in the last year'. The same applies to words like 'before', 'ever' etc. where you have to use the present perfect for as in ' I had never seen penguins before I went to the zoo in Toronto'.
    – Chris
    Nov 23, 2016 at 19:36
  • I was born. There is a use of the simple past, but the "impact still lies". This explanation, no matter how often it's repeated, is a bad one that I suspect causes much more confusion than it resolves. May 27, 2018 at 11:39

I'm glad I finally managed to understand the use of saw and seen:

saw = used when talking about the moment of speaking

seen= used when talking about something that happened in the past but the affirmation is being said in the present

I saw a cat (at the moment of speaking) I have seen a cat (affirmation said at the moment of speaking with the action of seeing the cat being on the past)


I saw a dog

In a specific time in the past, you saw a dog, and that is all you are saying unless previous/upcoming sentences reveal more.

Example: I saw a dog by that tree yesterday.

I have seen a dog.

On a regular, continual, or multiple basis in the past, you saw a dog, strongly implying more than once. You may see him again under the same circumstances.

Example: Over the past couple weeks I have seen a dog walking around.

Example: I have seen a dog get into your trash. - You might say this in response to seeing someone's trash on the ground, if you saw a dog do that before, and strongly suspect the dog did it this time.

  • 1
    Might "I have seen a dog" also indicate a single recent event? "Good morning, Jim. Climbing up the stairs to your place, I have seen a dog. I wonder who is the owner." Dec 14, 2014 at 5:31
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    @CopperKettle Yes, definitely. The have sentence just means that the event of seeing the dog is still relevant in the present.
    – Ben Kovitz
    Dec 14, 2014 at 5:33
  • 1
    In the original sentence, there is no implication of regularity or recurrence, although have can clearly mean that, as in your examples. That's one of many ways that seeing a dog can have happened in the past and still be relevant in the present. The simple past tense would mean the same thing in your first example (because of "over"). The distinction between past tense and present perfect in English is just horribly, horribly complicated.
    – Ben Kovitz
    Dec 14, 2014 at 5:46
  • 1
    The answer gives one possible difference in meaning, but appears styled as a complete and definitive answer. More likely to frustrate than help learners. Dec 14, 2014 at 6:52
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    It's all good. :) @CopperKettle - this is just my opinion and intuition here, but sometimes "I have X" can be used if the speaker/writer is talking about something that could be a regular/continual action, from the speaker's/writer's point of view or belief. So - Climbing up the stairs to your place, I have seen a dog - the speaker may have physically only seen the dog once, but is somewhat implying that he could see the dog again and again. So the cue is that the speaker believes the dog belongs there, and it is not some random dog.
    – LawrenceC
    Dec 15, 2014 at 0:51

I saw a dog.

This implies that the action happened at a point of time in the past. It might be ten minutes ago, yesterday, last week, etc.

I have seen a dog

This sentence still has a connection to now. For example "I've seen a dog, let's get away because it can bite us!"

  • You wrote this answer in 1914, but it has a connection to now (I'm finding it incorrect now). In fact, when we mention anything that happened in the past, it has a "connection to now": We are saying it now! May 27, 2018 at 11:43

I saw a dog.

This means that at some time in the past, there was an occasion when you saw a dog. It could have happened at any time from the origin of the universe to a nanosecond ago.

I have seen a dog.

This means that within some interval of time that started in the past and extends to the present moment, you saw a dog, perhaps once, perhaps multiple times. When the time interval began, and whether it makes sense to have seen a dog only once or multiple times during that time interval, must be inferred from context. The start of the time interval might be understood only vaguely.

Here are some examples:

  • If you're a veterinarian at work and it's noon, and you say “I have seen a dog”, the relevant time frame is probably this morning. In that situation, “I have seen a dog” would mean “I gave a medical examination to a dog sometime this morning.”

  • In ultrasawblade's example, the relevant time frame is approximately the past couple weeks. “I saw a dog get into your trash” means that you saw it happen once. “I have seen a dog get into your trash” means that you saw it happen at least once, maybe several times, recently enough that it's still important now.

  • If you are leaving a movie theater, and you say “I have seen a dog”, your listener will probably understand that you intend dog to mean “a bad movie”. In this situation, the relevant time interval starts with the start of the movie and ends now. If you say “I saw a dog”, your listener will more likely understand you to mean that you literally saw a four-footed animal just a moment ago.

What's happening here is that the present perfect can suggest a shift to different meanings of the words seen and dog. Since you are leaving a movie that has just finished, the time interval of the movie is natural to think of if you put a verb into the present perfect and the sentence can somehow be understood as a statement about the movie. You could use the past tense to say the same thing, but the fact that you chose the present perfect encourages your listener to notice a currently relevant time interval that ends in the present moment, and interpret the other words in your sentence accordingly.

That’s why you can never get a straight answer when you ask people what is the difference between the past tense and the present perfect. The time interval of the present perfect stretches to fit whatever time interval is appropriate to the situation, and that time interval influences the meanings of the other words. Reality has an endless variety of situations, so there's no way to describe all the ways that the perfect present can alter the meaning of a sentence.

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