Ought is followed by to and another verb: You ought to wear a raincoat in this weather. In negatives and questions it becomes You ought not to wear it/ You oughtn’t wear it; Ought you wear it?; Oughtn’t you to wear it? (formally, Ought you not to wear it?; very formally, Ought not you to wear it?).
Some people, however, are reluctant to use these negative and question forms. Americans, in particular, often prefer to use should: You shouldn’t wear it; Should you wear it? Shouldn’t you wear it? This is perfectly correct, although should expresses a somewhat weaker moral obligation than ought, and so may be less appropriate in such injunctions as You really ought not to/ should not treat him like that.
When ought introduces another verb, the to must come in between. A recent tendency is to omit the to, as in ?? You ought wear it. This is quite nonstandard. In negative sentences and questions, however- ? You oughtn’t wear it; ? Ought you wear it?– the omission of the to is fairly widespread, especially in American English, where it is perhaps on its way to acceptability.
To can still be left out, however, at the end of a sentence: Shall we write and thank them? We really ought (to). It is easy to forget the to when ought is combined with another verb: ? He ought and could have mentioned it. The correct form is He ought to and could have mentioned it or He ought to have mentioned it, and he could have.
Other nonstandard usages, though common in some dialects, are: ?? You didn’t ought I to wear it; ?? He hadn’t ought to; ?? Did I ought to wear it? ?? He really did ought.
Source: The right word at the right time