You can word it so that it is clear that the broader set of permissions includes the narrower set of permissions...
When administering user permissions for the Contact Information section of the site, there are three roles available: Guest, Contributor, and Administrator. The Guest role is able to view information, but cannot edit it. The Contributor role is able to view and edit information, but cannot deactivate or delete it. The Administrator role is able to view, edit, deactivate, and delete contact information.
Or you can word it in similar fashion to the following...
You can choose more than one role for the same user in the same section of the site. The system will grant the user whatever permissions are allowed by at least one of the roles assigned to that user in the relevant section.