Any Yes / No field can have a Boolean Type assigned to it. By default, each Yes / No field is given the Boolean Type “Yes / No”, but you can add others. For example, if you have a field called “Secure?”, you might add A Boolean Type for the field with values named “Secure” and “Not secure”.
Edit a type to set up its Values. A Boolean type can have two or three values: one for the True state, one for the false state, and an optional third on for the null “neither checked nor unchecked” state. If you want a Boolean field to have just two states, tick the Required box for that field.