Second-order logic

Second-order logic is a kind of way to figure out things. With second-order logic, you can use symbols to form equations, just like you can with math. These equations help you figure out things and make sure that everything makes sense. For example, instead of just saying "dog" you can say "all the things that are dogs" and use symbols to represent that. Then you can use those symbols to draw a picture and make sure all the pieces fit together.