When I opened my mouth, I just said rude things.

Apparently this sentence is ungrammatical, since ~たら sentences in the past tense cannot have actions performed "intentionally" by the speaker.


  1. I just wanted to confirm that if we change the sentence to the present tense, it suddenly makes sense in Japanese?


When I open my mouth, I just say rude things.

Is this the case? If so, the fact that this sentence suddenly becomes grammatical merely by changing the tense to present is quite perplexing!

  1. Is there an intuitive explanation for why intentional actions in past-tense ~たら sentences don't make sense? They seem to make good sense when translated into English (though I know English conditionals behave differently)?

EDIT: The source of this example sentence is this YouTube video (should start at 14m09s).

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  • 3
    Could you link us to the origins of these sentences and where you've seen that the first sentence is ungrammatical? 🙏
    – Francis
    Commented Jan 8, 2023 at 22:05
  • I think it is more about usage of 口を開く, which is used for habit of saying the same thing over and over again (e.g., complaining). PastTense+たら per se can be used for actions like 走ったら足が痛くなった. ('Action+たら+Action' may not be possible. I'm not sure though)
    – sundowner
    Commented Jan 8, 2023 at 23:52
  • Both sound weird because of つい. They become OK without it as sentences to talk about a person's habit in the past and the present, but 開いたら sounds like a dialectical variation of 開けば in both. You should compare a pair like ご飯を食べたら出かける and ご飯を食べたら出かけた.
    – aguijonazo
    Commented Jan 9, 2023 at 1:27
  • @Francis: I added the source of this example sentence to my question.
    – George
    Commented Jan 9, 2023 at 7:00

1 Answer 1


[V た-form]-ら puts focus on a point on the timeline, real or hypothetical, where some action or even has just completed. You focus this point because something happens then.

You might perform another action.



These are examples of the second verb denoting an intentional act by the same person as the first.

You might notice something.


The second verb is used in the past tense but it doesn’t denote an intentional act. This is also true when you say 部屋の窓が開いていることに気づいた as 気づく is not something you intentionally do.

Your action might cause another person to react in some way.



Your examples are both unnatural. You open your mouth to say something. You don’t start saying something upon completion of opening of the mouth. When I hear 口を開いたら, I would expect to hear something like this.


In all these cases, たら marks some change in the course of action or event. It works as a switch, so to speak.

Now, when you are talking about two consecutive actions actually performed in the past by the same person, such a switch is uncalled for and たら would sound completely out of place.

x ご飯を食べたら出かけた。

There are other ways to connect the two actions in logically more natural flows.



You can still use たら if the second action is something you would or could have done but didn’t.


In other words, if you use an action verb in the past tense like that, it would be interpreted as an unreal event.

Some dialects, such as Kansai-ben, use たら more liberally than the standard variant of Japanese. As a speaker of one such dialect, I find 口を開いたら失礼なことを言う (without つい) to be totally acceptable as a sentence about someone who habitually says rude things, but 口を開けば would be considered more correct, at least more formal, in standard Japanese. 口を開く is used in a figurative sense here. たら is usually used for a concrete instance.


I try to answer the questions asked in the comments below, though it's hard to answer "why".

When you say 宝くじに当たったら家を買う, you are putting yourself at the point (on a hypothetical timeline) at which you've just won a lottery and stating what you're going to do from that point. Hence the past tense for the first verb and the non-past for the second.

When you talk about a sequence of actions you (or anyone else) knowingly performed in the past from the vantage point of the present, you should have no reason to put yourself at or particularly focus such a point in the middle.

たら is followed by a verb in the past tense when the completion of the first action triggered some reaction or resulted in some discovery. It puts focus on the point at which you felt the impact of such an event. A second intentional action by the same person doesn't require or deserve such a focus.

  • Do you know why this rule has emerged though? What about "[V た-form]-ら putting focus on a point on the timeline, real or hypothetical, where some action or even has just completed" (almost like a switch) makes it unnatural to use for intentional actions performed by the speaker, but only in the past tense? If, e.g., "宝くじに当たったら家を買う" is fine, why is "宝くじに当たったら家を買った" suddenly not fine? In both cases, it seems like "winning the lottery" acted as the "switch point" time in when buying (or haven bought) a house suddenly is something that can follow, no?
    – George
    Commented Jan 11, 2023 at 20:34
  • If "ご飯を食べたら出かけた" is awkward, what if we changed it to "彼はご飯を食べたら出かけた"? It seems intuitively hard to understand what about talking about someone else makes it OK.
    – George
    Commented Jan 11, 2023 at 21:24
  • Thanks so much for that addendum! I think I am starting to understand what makes some of these past tense constructions so awkward.
    – George
    Commented Jan 12, 2023 at 2:49

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