Final answer:
A modification method changes the internal state of an object, while an accessor method provides access to the internal state without modifying it.
Step-by-step explanation:
A modification method is a method in object-oriented programming that changes the internal state of an object. It typically takes parameters and updates the values of the object's attributes. For example, in a class representing a bank account, a modification method can be used to withdraw or deposit money into the account.
An accessor method, on the other hand, is a method that provides access to the internal state of an object without modifying it. Accessor methods are used to retrieve the values of an object's attributes. Using the previous bank account example, an accessor method can be used to get the current balance of the account.