shouldもought toも、後者の方がより固い表現という以外には、ほぼ意味は同じです。日常会話ではもっぱらshouldを用います。ought toは道徳的な当為（「〜すべし」）を言う際などに用いられます。あとは無論、否定文（shouldn't/ought not to）や疑問文（Should I/Ought I to）を作る際の作法に違いがあります。 https://www.oxfordonlineenglish.com/should-ought-supposedto-hadbetter 2. Should vs. Ought to In meaning, ought to is exactly the same as should. If you can use should in a sentence, you can also use ought to..... There’s no difference in meaning. In both cases, the two sentences with should and ought to have the same meaning. However, there are a couple of differences in how you use ought to. First, ought to is more formal, more old-fashioned, and less common in modern spoken English. That means you probably won’t use ought to unless you are writing, or you want to sound very formal. Secondly, ought to has a slightly different form. Obviously, you need to add to. Also, the negative form is not generally contracted.