What's the difference?

[rachella]

Smoke may damage your health.
Smoke can damage your health.

The nurse has to take his temperature at midnight.
The nurse must take his temperature at midnight.

Sorry, I must leave now.
Sorry, I should leave now.
Sorry, I ought to leave now.

You shall finish it before you leave.
You will finish it before you leave.

Are there differences in meaning?

[/i]

[ngelim79]

To my thinking...
more or less, the meaning is same....

I am anxious to the difference, too!

[LarryLatham]

Yes, there are differences in meaning, and the differences exactly correspond to the meanings of the different modal auxiliaries you have in your example sentences. Find a good resource that will help you understand those meanings, and you will then know how to interpret your sentences.

Some textbooks are better than others at explaining the differential meanings of modal auxiliaries, so if the book you have doesn't satisfy you, go to your library and find a different grammar book, or ask your teacher for one. Some are quite good in this area. The COBUILD books should do well for you, but there are others too.

Good luck.

Larry Latham

[stephen]

Larry is right. A good dictionary and grammar guide are good places to start. Modals all deal with what is called in technical talk mood. This being in more everyday English the attitude of the speaker (or writer.) Thus different modals express a different perception on the part of the speaker/writer. Topics dealt with by the modals in your example are probability, possibility and level of obligation. (I should point out that this is by no means the full extent of what modals can express.)

Happy reading
Stephen

[El_Chivo]

To my knowledge there is no difference between "have to" and "must." "Can" and "may" are different in that the former indicates ability while the latter denotes either permission or possibility. "Can" is, however, a word in transition and is gradually becoming synonymous with "may" with regard to permission. Sticklers will insist on the distinction, but definitions change as common use (or misuse) changes.

Should and ought are synonyms (in the US) and indicate that the following action is advisable or nearly obligatory. Must indicates that the action is mandatory.

Shall versus will is tricky. In the US we rarely (very rarely) use shall and the rules regarding its use are arcane. To my understanding, shall is synonymous with will, but should only be used in the first person singular or plural. In other words, "I shall" means "I will" and "we shall" means "we will," but "you shall" would be incorrect.

[LarryLatham]

To my knowledge there is no difference between "have to" and "must."

I believe I'll have to take issue with you here, El_Chivo. If we look at these two items used negatively, we see that there must be a difference.

...don't have to

...must not

These are clearly not the same, which implies that must and have to are different somehow.

Larry Latham

[woodcutter]

I think once in a while people come out with a statement like

"I have to not smoke"

and I can't really see that it would differ significantly from "must not".

Sorry to quibble! Nice to see people being directed to the meanings of the lexical items themselves - though of course in most cases here the resulting difference is practically nil.

[LarryLatham]

I think once in a while people come out with a statement like

"I have to not smoke"

and I can't really see that it would differ significantly from "must not".

Sorry to quibble! Nice to see people being directed to the meanings of the lexical items themselves - though of course in most cases here the resulting difference is practically nil.

It's not a quibble, woodcutter. It's not always easy to see the difference with certain examples. However, it gets easier, I think, once someone points out the source of the difference.

In the case of must and have to, both, of course have to do with something that the speaker regards as necessary in some important sense. And that is why so often, observers believe that they are equal. But what is always different about them is the perceived (by the speaker) source of the necessity. In instances where the speaker chooses have to, he perceives that the necessity comes from the outside. Someone or something outside of himself creates the necessity. But where he chooses to say must, he is thinking that he himself is involved in creating the necessity.

So, in the (quite rare, I should think) case of a sentence like:

I have to not smoke.

...we can surmise that it is likely not himself who has caused him to not smoke. Instead, perhaps his doctor has impressed upon him the necessity of quitting, or maybe his wife, or even, maybe, it is a decision he has come to personally, but only after reading an article about how nasty it is for his lungs (he submits to the logic of the article).

But if he says: I must not smoke.

...we can assume that he, after thinking it over, has decided for himself that smoking is not something he wants to continue as part of his lifestyle. He has personally created the necessity to not smoke. Most likely, this is something he would only say, under his breath, to himself.

I have to go now, probably means if I don't go now I'll be late for class.
I must go now, suggests that I think it's time for me to go, for whatever reason.

A parent who tells her son, "You have to get a haircut.", perhaps it is because she is aware of the school rules regarding hair grooming. If she tells her daughter, "You must change your skirt!", it is likely because her real message is: No daughter of mine is going to wear a skirt that short to school! Of course, this can always be over-ridden by her saying something that explicitly clarifies the source of the necessity: "You have to because I say so!!!"

Larry Latham

[revel]

Good morning all.

Before reading all of Larry's arguements, I can say that I would have defined the difference in more or less the same terms, but it would have been the opposite: that "must" indicated superior forces while "have to" might come from one's own choice or outside. After reading what Larry has to say I can see where he is coming from, though I still am not sure if that's how I understand the difference. I sometimes explain that "must" carries more force, for its combination of sounds, especially the "st" at the end that we like so much, while "have to" with its soft "ha", that pleasant vibration of the "v" and the nice one-two rhythm takes a bit of bite out of the obligation. Say these two sentences to different people.

You must do the washing up.
You have to do the washing up.

Have to go iron some shirts. My choice, could tell the roommate to iron his own shirts, but well, I like doing it, the obligation to wear ironed shirts to work is his, not mine, but I offered so I have to go press and that's why I have to let you all go now.

peace,
revel.

[lolwhites]

A common question on this forum seems to be "What's the difference between sentence X and sentence Y", often with everything the same except 2 modals or verb patterns and no wider context given, as if sentences existed in isolation! We then tie ourselves in knots (myself included) trying to think up explanations and then arguing about them!!

The problem with this approach is that the pairs, or sets of sentences are almost invariably uses in which the structures under question are equaly valid as the context given reflects the similarities rather than the diferences between them. Students should be encouraged to look at other uses of the structures under consideration, in diferent contexts and in the negative as well as the positive. Who knows, they might actually learn something useful that way.

[El_Chivo]

Very tricky, dudes, but the negation argument is specious. . "Have to" isn't a phrasal verb. It isn't a modal auxilliary either. The verb is actually have, not have to, and, according to the American Heritage, it means must. So, when you say "must not," the auxilliary must isn't receiving the negation; the verb that follows is: not smoke, not go, not scream. The obligation is not negated; get it? With "do not have" you're negating theverb that indicates obligation (have) and the infinitive that follows is not negated: to smoke, to go, to scream. The result is that the positive forms are synonymous, but the negatives aren't.

I think the opposite of must is may, not mustn't, though I'm open to other suggestions.

Also, some of the arguments I'm seeing seem to ignore the fact that two words can be synonyms though all of their definitions may not be. And it may also seem very awkward to use one or the other in different instances, though sometimes they can be interchanged.

[LarryLatham]

Very tricky, dudes, but the negation argument is specious. . "Have to" isn't a phrasal verb. It isn't a modal auxilliary either. The verb is actually have, not have to, and, according to the American Heritage, it means must. So, when you say "must not," the auxilliary must isn't receiving the negation; the verb that follows is: not smoke, not go, not scream. The obligation is not negated; get it? With "do not have" you're negating theverb that indicates obligation (have) and the infinitive that follows is not negated: to smoke, to go, to scream. The result is that the positive forms are synonymous, but the negatives aren't.

I think the opposite of must is may, not mustn't, though I'm open to other suggestions.

Also, some of the arguments I'm seeing seem to ignore the fact that two words can be synonyms though all of their definitions may not be. And it may also seem very awkward to use one or the other in different instances, though sometimes they can be interchanged.

Hmmmm. Possibly so. I've never seen it analyzed in quite this way before. Suppose we look at it again in some detail.

I'll grant that "have to" is not a phrasal verb, though it's tempting for all of us to sometimes present it that way, however innocently, simply because of its apparent contrast (or, for many, apparent synonymity) with must. We know that because, if we remember that English is fundamentally a SVC language, and then look at a sentence like:

I have to (not) smoke.

...we can see that if the verb in this sentence were have to, then the rest of the sentence (other than the subject) would still have to be classified as a verb, which cannot, by itself, serve as a complement after another verb. On the other hand, if the verb is have, then we see that the to attaches to smoke, forming an "infinitive with to", which we can understand as a verbal. Verbals can indeed serve as noun complements in a sentence. (Pardon my prattle about fundamentals we all know, but my brain seems to work better when I retrace the obvious, sometimes. ) I suppose our confusion is compounded from looking at the very common truncated versions: I have to! You have to! He has to! These appear, at first blush, to be complete Subject/Verb sentences on their own.

I'll also grant that have to is not usually a modal auxiliary, although when it is used as in the example sentence above, a reasonable case could be made that it is. One of the defining characteristics of modal auxiliaries is that they are movable, and in negations always immediately precede the word "not". Thus She can go is negated as She can not go. In our example sentence above, have to operates in the same way (which probably is why it seems a little wierd, and probably would be quite rare). But let's recognize that this is not a common way to use have to. Much more usual would be, You have to wear your heavy socks, or She has to take a test tomorrow, or Bill has to join the Army, or We'll have to call a plumber. Actually, this last example helps to prove beyond question, I think, that have to cannot be a modal auxiliary (in this sentence, at least) because it co-exists with will, and two modal auxiliaries cannot reside in the same clause.

There is other evidence as well for have to not being either a phrasal verb or a modal auxiliary. This is not a comprehensive argument!

But I'm having trouble reconciling the rest of your contention, El_Chivo. Far be it from me to argue with American Heritage that have means must. I'm not that bold. But I think we have to be careful just how we interpret what AH means by "have means must". We would be mistaken if we believe that they are identical, and although I have not consulted AH in this instance, I'd be willing to bet that they have a robust disclaimer counselling caution to the reader against too literal an interpretation of the equality. If they were identical, then we could substitute one for the other, but we've already seen that we cannot. What we can sometimes do, in particular and explainable instances of use, is substitute must for have to. But, I submit, that does not mean that the full meaning of the alternate utterances is identical. So, while I won't disagree with your description above of which word is negated and which is not with regard to must and have to, I'm afraid I cannot buy your conclusion: "...the positive forms are synonymous, but the negatives aren't."

Swan (p. 284), who most generally tells things in ways I can get behind, seems to support my argument (actually, I guess it's the other way around, since he wrote the book before I made the argument ) that must and have (got) to are similar, but not quite the same. He says that the obligation implied with use of either of them seems to come from the speaker if she chooses to use must, and from outside if the speaker chooses have (got) to. I have found that the distinction seems to be clear in my mind whenever I've looked closely, as long as I'm willing to see apparent reality of meaning in the uses of either phrase in context. I guess what I'm saying is: the distinction works for me, and it works all the time. It also easily explains (to me and to my students) when to use must and when to use have to, or how to interpret the particular meaning when one hears or reads them. It easily explains why our example sentence above, "I have to not smoke" sounds funny, but "I must not smoke" doesn't. (Although the former would be perfectly understandable if, in the context, it really means: "I have been told not to smoke.") But I also can see that it sometimes takes a certain flexibility of interpretation in some contexts, and perhaps not everybody is prepared to grant that flexibility.

Larry Latham

[woodcutter]

So "have to" has a tendency to be used for an obligation imposed by others? In regards to the original question, this is not relevant. The sentences about the nurses have been supplied, context free. We may guess that the use of "must" in the original example is not very natural. Not every utterance is. I do not think we can use our knowledge to make any guesses about the difference in context between the two original sentences. As far as we can tell, it is a synonym.

[LarryLatham]

So "have to" has a tendency to be used for an obligation imposed by others? In regards to the original question, this is not relevant. The sentences about the nurses have been supplied, context free. We may guess that the use of "must" in the original example is not very natural. Not every utterance is. I do not think we can use our knowledge to make any guesses about the difference in context between the two original sentences. As far as we can tell, it is a synonym.

Can't go along with you here, I'm afraid, woodcutter. The original question, if I'm interpreting correctly, was: "Are there differences in the meanings of sentences that are identical except for different modal auxiliaries?" And one of the issues arising in the attempt to answer the question was: "Is have to one of the auxiliaries to be considered here?" Since have to is often (mistakenly, I believe, because for one thing it isn't even a modal auxiliary, as our friend El_Chivo has pointed out) offered as a synonymous alternative to must, which is uncontroversially a modal auxiliary, it rightly belongs in this discussion. So the (very strong, in my opinion) tendency for have to to indicate an obligation or necessity imposed from outside the speaker is not only relevant, but right on the mark, as I see it.

We may guess that the use of "must" in the original example is not very natural.

I'm sorry, but I don't understand you here. The original example using must seems to be: "Sorry, I must leave now." Since it has been supplied "context free", we are left to imagine any kind of context where it might become a natural utterance. I can, and in the context of my imagination (having been stopped on the street by a too talkative salesman who wants me to buy a "rolex"), the supplied sentence sounds OK (read natural) to me.

Not every utterance is.

Now here I have no quibble with you. Complete agreement!

I do not think we can use our knowledge to make any guesses about the difference in context between the two original sentences. As far as we can tell, it is a synonym.

Which two original sentences did you have in mind, woodcutter?

Larry Latham

[LarryLatham]

Ah...OK! On re-reading the original post, I think I see where you're coming from, woodcutter. I overlooked the use of must in the pair of sentences about the nurse. That also clears up which two sentences you have in mind.

But I still don't think I can accept your conclusion that these sentences are synonymous. These two sentences, for me, are not alternatives to be used in the same speaking situation, having identical meaning. Each has its own proper context, if it is to seem natural.

The first: "The nurse has to take his temperature at midnight" might be natural if, say, a family member of the patient is talking to another family member about the nurse's routine of care. The choice of has to is, I believe, driven by the source of the necessity seen to be external to the speaker.

The other: "The nurse must take his temperature at midnight" would not be natural in that same context. But surely it would if the patient's doctor was talking to the nursing supervisor about the necessity of a timed regularity of temperature taking. Here the doctor demanding the specified timing and the speaker are one and the same.

Larry Latham