Depending on the context, the verb must can be used performatively. The verb have (to) cannot very easily with third person Subjects. What I mean by performatively, is that the actual uttering of the sentence is not a description of the necessity, but a directive, whereby the speaker is exerting their authority over the Subject just by uttering the sentence. The sentence causes the obligation, it doesn't merely describe it. If a speaker says:
- Passengers have to fasten their seat-belts.
This is likely to be taken as a description of the fact that passengers must fasten their seat-belts.
However, if a speaker says (i.e. in this case writes):
- Passengers must fasten their seat-belts.
This is likely to be taken as a directive whereby the reason that they have to fasten their seat-belts is because I'm telling them so in this utterance.
I disagree with the idea that have to is because of a third party saying so. The issue is that with must the speaker is yielding to the authority of some other obligator, or is obligating something themselves. Have to may represent some type of decree but the presentation is not one of obligation, but just necessity.
It can help to bring out this difference if you consider things that are necessary, but involve no morality, authority or obligation. For example:
- You'll have to use this key to get into the house.
- You must use this key to get into the house.
The first sentence seems to just be saying that this key is necessary for the purposes of entering the house, but there's no coercion, authority, morality or obligation involved. In the second sentence, the speaker seems to be saying something about some obligation to do things this way.
Understanding how modal verbs are used is very complex. I am not saying that any of these things are core meanings of these verbs. But they describe the implications that using these verbs often has.
"[...] questionable and unsafe places to sleep had plunged him into a constant alertness, one that had only been reinforced when [...]"
Grammatical, but weakly written.
*EDIT - questionable = unsafe. you risk watering down the sense of danger. had plunged - why past perfect? also, hyperbole? Constant alertness - if you are not continuously [in focus], could you be said to be alert? Been reinforced - passive is OK, but why? (and, lose tempo.)
"After what he perceived to be an uncertain amount of time [...]"
Grammatical.
"The noise paused in front of the door"
Grammatically correct, semantically invalid, for the reasons you stated. Prefer "the noise stopped"
can a sound "gain proximity" ? (i.e getting closer).
Prefer "draw nearer" or, simply, "intensified," or the like
"[...] he caught a glimpse of a small group of guards facing the door. Somewhere in his mind, he noted their unusual numbers, though it barely sparked any curiosity in him"
Numbers --> Number, singular: a large (unusually large) number
Prefer switch "it" with "this" to reinforce predicate.
"his thoughts had been slowed down to a halt by the bland nature the days had acquired."
Grammatical, but weakly written.
*EDIT - 1) idiomatic and uninspired. This is no place to make suggestions, but as you have asked, why not: "Time now ran together and his thinking, not at all. Yesterday, today, tomorrow: mere words, no longer concepts, no longer tied to anything, any anchor, of sense and sensing. His Being bled through the fifth dimension listlessly..."
Best Answer
"can you not," is a British English, albeit somewhat archaic dialectal pattern. Ashworth is correct that the spelling “traveling” implies the advertisement is not British (“travelling” would be). In America, the word honor, versus British honour. The change in spelling, only occurs if the speaker/writer catches themselves, or another points it out.
The phrase is used like this: Can you not call her? With the emphasis on the word not. The sentences do look strange placed side by side. The first is an advertisement (business). Followed by the second sentence, asking a personal and challenging question (inappropriate usage for business). It is a 2021 advertisement attempting to be personal.