What Is Their Main Difference?
The main difference between 'ought to' and 'could' is that 'ought to' is a semi-modal verb while 'could' is a modal verb.
'Ought to' is a semi-modal verb. Semi-modal verbs sometimes act like modal verbs and sometimes act like a main verb. For example:
'Could' is also another well-known modal verb. To put it simply, 'could' is the past tense of 'can.' It is used to talk about abilities, request something, etc. For example:
Talking about Possibility
We use 'ought to' and 'could' to talk about possible events.
- 'Could' expresses slight possibilities that we are uncertain about their accuracy:
- 'Ought to' expresses what we assume will happen and we have a higher level of certainty than 'could:'
Talking about Obligations
'Ought to' is used to talk about duties and obligations that are motivated by law, society, someone, or oneself. 'Ought to' is uncommon and its usage has lowered significantly. 'Must' often replaces it when expressing obligations. Have a look:
Talking about Abilities
We use 'could' to talk about what we were able to do. These are past abilities that we no longer possess or the person with the ability has been deceased. For example: