I didn't reply to a ping in the chatroom.

The English enthusiast suggested this about me at the time:

  1. He must have already slept.

Hours (and dreams) later, I came back, I saw the above sentence, and I wrote that it suggests that he is no longer sleeping (he finished sleeping), and so wasn't grammatical at the time it was written, and should have been, for example, He must have already gone/went to sleep/bed.

But we know that the perfect aspect can generally be used when a state or action continues into the present. So the English enthusiast wonders why not must have slept in this context?

Does already make a diffrrence? Does the modal must make a difference? Are my ideas American-glish?

Further, he asks about

  1. He must have [already] been sleeping.

in the same situation. I replied That no workie, neither and that we won't say that when we assume that he continues to sleep at the time we utter it. We need, I say: He must [already] be sleeping.

But I can't explain why.

In the context: What's wrong with 1? What's wrong with 2?

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  • He must have already gone to sleep/bed
  • He must [already] be sleeping
  • He must be asleep already

Any of the above can express the idea of a person who is either in bed or sleeping at the moment of speaking.

The modal verb must is used for speculating, and making deductions. It expresses the speaker's conviction or certainty. In other words there is no other possible or logical explanation as to why the OP hasn't replied to the ‘ping’.

In the present simple: “He must [already] be in bed”, or “He must [already] be sleeping/asleep.”

The present perfect is used to express this deduction in the past. The OP was not ‘there’ and if the hour was particularly late, we are left with no choice but to say: “He must have gone to bed.” The verb “gone” tells us that the person is now somewhere else.
Here's another example:

A: Where's Suzie?
B: She's gone to the dentist.
A: When's she coming back?
B: She'll be back by noon.

At 11.30 am this conversation might occur

A: Is Suzie back?
B: Yes, she's already back from the dentist.

The adverb already tells us that Suzie is back earlier than we expected.

In the OP's sentence

  1. He must have [already] slept.

The action of sleeping is completed. The placing of already in that sentence is redundant and sounds slightly awkward; it does not significantly change the meaning. Given the choice, I would leave it out. However, it's important to emphasize that the person in question is now awake.

  1. He must have been sleeping.

Sentence two is only repeating the same concept but using the present perfect progressive tense.


In “He has been running” the sentence suggests the person mentioned has finished running. Perhaps now he is hot and sweaty and needs a shower. “He's already been running” suggests that the person has returned from his running session.

  1. He must have [already] been sleeping

Suggests that the action was happening before a subsequent incident, i.e. the friend ‘pinging’ him in the chatroom.

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  • How about He must have had that car for over a year now? Or He must have been sleeping for over an hour now? – Araucaria - Not here any more. Apr 27 '15 at 10:24
  • @Araucaria what about it? By mentioning the length of time, you're saying how long the action MUST HAVE been taking place. I know you're itching to answer this post, you might as well :) – Mari-Lou A Apr 27 '15 at 10:30
  • @Mari-LouA I can't answer this post! I'm not sure what the answer is :-) But I'm not sure that using must have necessarily means that this action's finished .... It's a toughie :) – Araucaria - Not here any more. Apr 27 '15 at 10:33


Present (and recent) time:

a. He must be asleep [already].

b. He must be sleeping [already].

c. [I think that] he must have [already] gone/went to sleep/bed.

d. He must have been sleeping for the last eighteen hours [before now], if he has not heard that.

However, I will contend that c and d in the above are rare, and that "must have" is much more commonly related to past events.

Past time:

a. By that time, he must have [already] gone/went to sleep/bed.

b. By that time, he must have [already] been sleeping.

c. He must have been sleeping for the last eighteen hours [before that time (in the past)], if he had not heard that.

Thus, the problem with the verbs in 1 and 2 is that they're usually made for past time, while the application required something appropriate for present time.

And the modal + "have/perfect infinitives" makes for a difference: when using "have/perfect infinitives" you are not getting the connection with the present that is created by the present perfect. With the modal + "have," you're describing events that are mainly in past time.

Expert commentary

Modality and the English Modals By F.R. Palmer

The modal verbs are not normally used, therefore, in past tense forms to refer to past judgments. Past tense forms are normally tentative with present time reference. It is, of course, possible to report past judgments, but this requires verbs such as THINK. BELIEVE, etc.

In contrast, the proposition can be in the past, for we can make judgments about past events. This is achieved by the use of have before the main verb:

Well, he must have been flying too low. (W.5.3.n6)


Davidsen-nielsen:tense and Mood in Engl. Tiel 1: - Page 167 Niels Davidsen-Nielsen - 1990

'I must have been in the garden when you called.'

By using the present perfect in examples like these the speaker informs the addressee that on the basis of present time evidence it is his conclusion that a certain event has taken place.


The New Cambridge English Course 3 Teacher's Book By Michael Swan, Catherine Walter, Desmond O'Sullivan

Modals with perfect infinitives: You may need to remind students that most modal verbs (e.g. should, must, may, might) do not have normal past forms. However, a special structure is possible in which the modal verb is followed by a perfect infinitive (should have gone, might have been). These forms are used to talk about events and situations (usually past) which did not take place or which are not known for certain to have happened.

This reference further shows that "must have" is mainly used in past time in both AmE and BrE: American and British English Preferences: Spelling, Grammar, Punctuation ... By Nancy Salama, Mary Ghali

Related samples

The Mirror of Parliament for the ... Session of the ... ... John Henry Barrow - 1834

Mr. O'CONNELL.— Honourable Gentlemen must have been sleeping for the last eighteen years, if they have not heard that.


  • And why can't He must have been sleeping describe the present? It is the present perfect tense, after all.

No, it's not the present perfect in all cases. It's mainly a modal form that is related to the past.

Now, one could reply on the phone:

Sorry to answer only now. I must have been sleeping at my desk.

and then it has a present perfective meaning.

But in general see this ESL teaching expert and moderator here:

Must + present perfect (which is one of the modal perfects) means that the speaker or writer is sure that something happened or didn't happen in the past.

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  • 1
    Thanks Marius! But it doesn't seem to answer the questions. – Jim Reynolds Apr 27 '15 at 7:03
  • 1
    "Must be gone to sleep" is certainly unidiomatic if not incorrect. "Right now, he must have gone to sleep" is better. Which just happens to be the same as "By that time, he must have gone to sleep," so must must have changed tense to mean "had to" rather than "has to". – Andrew Leach Apr 27 '15 at 7:10
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    I am not sure that he must be gone to sleep is idiomatic. And why can't He must have been sleeping describe the present? It is the present perfect tense, after all. My friend and I are both fairly knowlegeable, and we are looking for detailed answers. – Jim Reynolds Apr 27 '15 at 7:17
  • He must be gone to sleep is definitely not idiomatic. Perhaps the writer means he must be asleep. – WS2 Apr 27 '15 at 7:37
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    How about He must have been sleeping for over an hour now? – Araucaria - Not here any more. Apr 27 '15 at 10:08

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