'Agree to' v/s 'Agree with'

While there can be a fairly lengthy explanation of when to use 'agree with' and 'agree to', the following simplified rule should suffice for the GMAT:

Rule: You agree 'with' a noun and you agree 'to' a verb.

Examples:

1. John agrees with his brother. ('brother' is a noun so agree 'with')
   
   
2. John agreed to run an extra mile. ('run' is a verb so agree 'to')
   
   
3. The manager agreed with the proposal. ('proposal' is a noun so agree 'with')
   
   
4. The manager agreed to open the office on Sundays. ('open' is a verb so agree 'to')

In short you agree 'with' something but you agree 'to' do something.