Indispensability of 'to' after 'ought' in British English [closed]

SUMMARY: While Americans don’t always have to use the to after ought in negative contexts, the English apparently must do so everywhere, even negatively.

The word ought can today act as a true modal auxiliary only in negative contexts, which includes interrogative ones albeit in a super-formal register.

By true modal, I mean it acts exactly like must does in that:

1. It does not inflect for tense. There is no distinction between past and non-past.
2. It does not inflect for third-personal singular present, so there's never an -s.
3. It takes a bare infinitive, not a to-infinitive.
4. Its contracted negative undergoes subject–verb inversion dragging the negative particle along with it: Oughtn’t he ...

Negative examples taking a bare infinitive

• One ought never add a to particle to this sentence.
• Never ought one add a to particle to this sentence.
• He oughtn’t bother her today.
• You told me he oughtn’t bother her yesterday.
• Oughtn’t she call him?
• Ought she call him?

Positive examples taking a to-infinitive

However, in non-negative/interrogative contexts, we must relax modal trait #3 above and supply said particle.

• One ought to add a to particle to this sentence.
• He ought to bother her today.
• You told me yesterday that he ought to bother her.
• She ought to call him.

The positives all take a to particle, but the other modal properties still apply.

See also the other two semi-modals, need and dare, for the circumstances under which they, too, behave like full modals.

Indispensability?

In your example from your comment:

Your skin color ought not *to dictate your future.

That is not something I can say in my own private idiolect, because for me the not needs to cancel the to for me:

Your skin color ought not dictate your future.

The other way sounds super old-fashioned to me. I understand that some green and pleasant pockets of England may still use the to-infinitive version in positives, though.

Corporal research has suggested that skipping the to for negatives and interrogatives is no longer the more common way of doing things, and that most people put it there “obligatorily” even in negatives and interrogatives than those like me who do not. There are still a few of us, however. See next.

Citations

Here are a few Google books citations that forego the to particle in negatives:

• If a goal is wrong, we ought not try to achieve it. Only if it is right, ought we to try.
  —Aristotle for Everybody, Mortimer J. Adler, 1997

• Sometimes "ought" means what one should do, all things considered — as in "In these circumstances what you ought to do is start over" or "Given the situation, I think you ought not press your right to x."
  —Ethics in Engineering Practice and Research, Caroline Whitbeck, 1998.

• 1.Scientists ought not do research that causes unjustified risks to people. 2. Scientists ought not do research that violates norms of free informed consent. 3. Scientists ought not do research that unjustly converts public resources to private profits.
  —Ethics of Scientific Research, Kristin Sharon Shrader-Frechette, 1994.

• A normative rule (for example, "one ought to do A given B") is defeasible in a normative system S iff S contains another rule to the effect that one ought not do A given B&C or one is permitted not to do A ...
  —Defeasible Deontic Logic, Donald Nute, 1997.

• The lover of art who doesn't feel at ease when confronted with contemporary art ought not attack it, nor should he force himself to take pleasure in it.
  —Soul of the Age: Selected Letters of Hermann Hesse, 1891–1962, Therodore J. Ziolkowski, 1991.

• He cringed to remember them meeting in the Circle Ritz lobby this late morning, both of them looking like they had been for a long time somewhere they oughtn't admit to.
  —Cat on a Hyacinth Hunt: A Midnight Louie Mystery, Carole Nelson Douglas, 1999.

• Shouldn't she, if she believed that I took pleasure in cruelty, want not to be with me, oughtn't she be afraid of the pain I'd caused her?—
  —First Love and Other Sorrows: Stories, Harold Brodkey, 1998.

• Recognizing that a consistent and uniform approach to surrogacy was needed, the ministers agreed that "there were too many unknowns, too many uncertainties and that we oughtn't experiment ...
  —Women as Wombs, Janice G. Raymond, 1993.

• He put down his rifle, walked over, and grabbed the other end of the saw. In no time at all the two men zipped through the logs. "After all," he said later, "it was cold and one man oughtn't work a two-man saw.
  —Stark Decency: German Prisoners of War in a New England Village, Allen V. Koop, 2000.

• Hermann Hesse - 1971 Oughtn't so early an event as the Munich Putsch have shown them what he was?
  —If the War Goes on: Reflections on War and Politics, Hermann Hesse, 1971.

I must point out that although examples of fully modal ought like these can be found in recent publishings, they are in the minority, and more people today now use a to-infinitive even in negative and interrogative context than, like these, do not.

Transatlantic Differences

As explained here, Quirk et al. in A Grammar of Contemporary English report that American English sometimes does exactly what I have just explained:

Ought regularly has the to-infinitive, but AmE occasionally has the bare infinitive in negative sentences and in questions (although should is commoner in both cases):
- You oughtn't smoke so much.
- Ought you smoke so much?

On the other hand, noted English authority ^:–) Barry England here reports that:

British English requires the to-infinitive. (I didn't know until reading the above comments that American English allowed its omission.)

I will leave it to others to trace the history of this.

What is special about the modal auxiliary 'ought' is that it takes the 'to infinitive' after it.

Ought to

from English Grammar Today (http://dictionary.cambridge.org/grammar/british-grammar/modals-and-modality/ought-to)

Ought to is a semi-modal verb because it is in some ways like a modal verb and in some ways like a main verb. For example, unlike modal verbs, it is followed by to, but like modal verbs, it does not change form for person:

I ought to phone my parents.

It ought to be easy now.

Ought to: form Affirmative

Ought to comes first in the verb phrase (after the subject and before another verb):

We ought to do more exercise.

Ought to cannot be used with another modal verb:

Medicine ought to be free.

Not: Medicine ought to can be free. or Medicine can ought to be free.

Negative

The negative is formed by adding ‘not’ after ought (ought not to). It can be contracted to oughtn’t to. We don’t use don’t, doesn’t, didn’t with ought to:

We ought not to have ordered so much food.

Not: We don’t ought to have ordered so much food.

You oughtn’t to have said that about his mother.

Not: You didn’t ought to have said that about his mother.

The negative of ought to is not common. We usually use shouldn’t or should not instead:

You shouldn’t speak to your father like that. (preferred to You oughtn’t to speak …)

Also from Practical English Usage by Michael Swan: