What is the difference between Input types and Object types in GraphQL mutations?

In GraphQL, you cannot use regular object types as mutation arguments — you must use input types. Input types are declared with the input keyword and can only contain scalar types, enums, or other input types (not object types with resolvers). Example: input CreateUserInput { name: String! email: String! } used as createUser(input: CreateUserInput!): User. The reason for this distinction is that object types can have arguments on their fields (resolvers), which does not make sense for inputs. Input types are pure data containers, while object types are resolved data with behavior. Using a single input object argument (instead of many positional args) also makes mutations more forward-compatible.