Learn English – Difference between “Should” vs “ought to”

The primary difference between the two is in the implication of the result.

"You should" carries the connotation that if you do as suggested, the outcome will be favorable; it puts the focus of the statement on a positive consequence. You could say that it is an encouragement to engage in good behavior.

"You'd better", on the other hand, carries the connotation that if you fail to do as suggested, the outcome will be unfavorable; it puts the focus on the negative consequence. You could say that it is a warning about engaging in bad behavior.

If the phrases were extended, you would almost always see something along the lines of

You should wear a coat, so you can stay warm

vs.

You'd better wear a coat, so you don't get frostbite.

I must disagree with both user37324 and NOAD.

A recent survey of literature and corpus study¹ on this topic shows clearly:

• that the factors favouring choice of ought to over should are syntactical rather than semantic, and
• that ought to is found more often in speech than in writing, but
• in all contexts, should is preferred, by factors ranging (depending mostly on syntactic context) from 1.9 to 12.6 to 1.

These findings for British English coincide with my own impressions of American use, and with the quantitative findings of American corpus studies. I do not hesitate to assert that the two terms are synonymous. Should may be used in any context where ought to may be used.

And since should is far more frequent, I believe that a Learner may safely eliminate ought to from his vocabulary altogether; using should rather than ought to will never be wrong—unless the Learner must conform to a contrary opinion expressed by an examiner or academic advisor!

¹Cappelle, Bert and Gert Desutter. 2010. ‘Should vs. Ought to’. In: Bert Cappelle and Naoaki Wada (eds.), Distinctions in English Linguistics, Offered to Renaat Declerck. Tokyo: Kaitakusha, 92-126.