The concept of ‘force’ is abstract and challenging for many physics students, and many studies have
 revealed misconceptions that hinder students’ understanding and learning in classical physics. One reason
 for this may be the multifaceted nature of the concept and how textbooks give different definitions
 and explanations depending on the context. In this article, we present a framework of eight categories
 for how the concept is described, based on fundamental principles in physics, their historical sources
 and an analysis of how ‘force’ is described in four physics textbooks used in upper secondary schools in
 Norway. Examples from one of the textbooks that constituted the empirical basis for the framework are
 given. These reveal that textbooks may present students with a variety of definitions and explanations
 of ‘force’. It is argued that students should be made aware of this variability in order to support their
 motivation and learning in physics, but also to understand the complex and evolving nature of the force
 concept and other important concepts in physics.