"Ought to" is used to advise or make recommendations. "Ought to" also expresses assumption or expectation as well as strong probability, often with the idea that something is deserved. "Ought not" (without "to") is used to advise against doing something, although Americans prefer the less formal forms "should not" or "had better not."
You ought to stop smoking. recommendation
Jim ought to get the promotion. It is expected because he deserves it.
This stock ought to increase in value. probability
Mark ought not drink so much. advice against something (notice there is no "to")
Using "Ought to" in Present, Past, and Future
Most modal verbs behave quite irregularly in the past and the future. Study the chart below to learn how "ought to" behaves in different contexts.
Positive Forms 1. = Present 2. = Past 3. = Future
Negative Forms 1. = Present 2. = Past 3. = Future
ought to recommendation,
1. Margaret ought to exercise more.
2. Margaret ought to have exercised more so she would be better prepared for the marathon.
3. Margaret ought to come to the fitness center with us tonight.
1. Margaret ought not exercise too much. It might cause injury.
2. Margaret ought not have run the marathon. She wasn't in good shape.
3. Margaret ought not stay at home in front of the TV. She should go to the fitness center with us.
ought to assumption, expectation, probability
1. She ought to have the package by now.
2. She ought to have received the package yesterday.
3. She ought to receive the package tonight.
"Ought not" is used primarily to express negative recommendations. (See above.)
Notice "Ought not"
Remember that "ought to" loses the "to" in the negative. Instead of "ought not to," we say "ought not." "Ought not" is more commonly used in British English. Americans prefer "should not."
You ought not smoke so much.
She ought not take such risks while skiing.
They ought not carry so much cash while traveling.