大体上两者的意思是相同的,通常可以互相转换。ought是助动词，不是过去式。

二者区别：ought to比should 语气强（1）should 表示主观看法，一些建议，劝说时，译作“应当”。

ought to，直接接动词原形，更多反映客观情况，“有义务”或“必要”做某事，译为“应当，应该”（2）ought to的否定就表示做某事一定是错误的而should的否定就表示某动作不一定要做3.should可以用于虚拟语态,而ought to 不能ught to 是唯一一个可加to的情态动词!ought to 比should语气更强烈ought to的否定就表示做某事一定是错误的而should的否定就表示某动作不一定要做表示应该，责备时 区别不大 但是should可以在名词从句中表示虚拟如在suggest,advise,等从句中 在lest,for fear that, in case等的状语从句中也只用should 另外should有表示惊讶之意ought to与should意思接近，大多数情况下二者可以互换，但是should谈的是自己的主观看法，ought to则更多反映客观情况，在谈到法律、义务和规定时使用。如： We should／ought to help each other and learn from each other in our work．She is your mother, so you ought to support her．We ought to go and see Mary tomorrow, but I don’t think we will．ought to具体用法如下：1. (表示义务、责任等) 应当, 应该You ought to work harder than that.2. (表示劝告、建议等) 应该, 该You don't look well. You ought to go to see the doctor.3. (表示猜测、期望) 总应该，理应It ought to be a fine day tomorrow morning.4. “ought to + have + 过去分词”表示过去应做某事而实际未做You ought to have told me that (but you didn't).这时ought to和should可以互换使用。二、ought to的否定式和疑问式1. ought to的否定形式是ought后直接加not构成，其否定形式可缩写为oughtn't。One ought not (oughtn't) to cross the street against the red light.2. ought to的疑问式是将ought提到句首构成。

—Ought we to do it at once? —Yes, you ought to.在反意疑问句里，下面两种形式都可以：He ought to be here now, shouldn't (oughtn't) he?"必须 ,应该, 应当"的意思，ought to与should意思接近，大多数情况下二者可以互换，但是should谈的是自己的主观看法，ought to则更多反映客观情况，在谈到法律、义务和规定时使用。ought to具体用法如下：1. (表示义务、责任等) 应当, 应该You ought to work harder than that.2. (表示劝告、建议等) 应该, 该You don't look well. You ought to go to see the doctor.3. (表示猜测、期望) 总应该，理应It ought to be a fine day tomorrow morning.4 “ought to + have + 过去分词”表示过去应做某事而实际未做You ought to have told me that (but you didn't).这时ought to和should可以互换使用。ought to的否定式和疑问式ought to的否定形式是ought后直接加not构成，其否定形式可缩写为oughtn't。

One ought not (oughtn't) to cross the street against the red light.2. ought to的疑问式是将ought提到句首构成。