We use “agree with” when we are with a person or an opinion that a person shares. We use “agree on” when two people reach an agreement about a certain topic. We use “agree to” when there is an action that must follow the agreement.
I agree with Peter, we should buy the company.
We never agree on which road to take.
I agreed to take the bus instead of driving.
We usually use “agree with” when we are agreeing with a person
I agree with you
John agrees with Michael.
You can also “agree with” a statement or opinion as you are implicitly saying that you agree with the person.
I agree with the idea of going to the cinema this evening.
We usually use “agree to” when you agree to something like a compromise or a contractual agreement.
Michael agreed to take out the trash on Wednesdays.
I agreed to sell the company as long as John doesn’t buy it.
We use “Agree on” when we want to emphasize the topic or point made in a debate.
I agree on the issue of increased pay benefits but not on dental care.
They don’t agree on anything.
It is often implied that the people “agree with” each other and then the preposition “on” introduces the topic about which they agree on.
I agree with you on the issue of increased pay benefits but not on dental care.
They don’t agree with each other on anything.
Agree On and With difference
To “agree on something” is often used after a discussion and about a certain topic of that discussion. It is more commonly used when two people agree together.
At least we agree on the first part.
“To Agree with something” is often about a statement, idea, or opinion. “Agree with” is used more often to say “I agree with you” and your opinion on this subject.
I agree with the first part.
There is a certain amount of overlap where agree on or agree with could both be used.
We both agree with the first part.
We both agree on the first part.
You can also use “agree about” in the same situation as “agree on” but it is less common.
They don’t agree about the introduction of a carbon tax.
Agree That (+ No preposition)
Sometimes we don’t use a preposition but rather start a new clause describing what it is we agree on.
I agree that taking the car is the best idea.
We agree that I should be the one who looks after the Jefferson report.
“Agree Upon” is often used in a more formal situation after the fact.
The budget has been agreed upon by all the ministers involved.
“Agreed-Upon” functions as an adjective to describe a previous agreement.
That is not the agreed-upon procedure that we signed in our contract.