 More generally, we can now see that there are in fact two different dimensions along which one’s notion of a constraint might be broader or narrower. A first dimension is that of the source of a constraint — in other words, what it is that brings about a constraint on freedom. We have seen, for example, that some theorists include as constraints on freedom only obstacles brought about by human action, whereas others also include obstacles with a natural origin. A second dimension is that of the type of constraint involved, where constraint-types include the types of internal constraint just mentioned, but also various types of constraint located outside the agent, such as physical barriers that render an action impossible, obstacles that render the performance of an action more or less difficult, and costs attached to the performance of a (more or less difficult) action. The two dimensions of type and source are logically independent of one another. Given this independence, it is theoretically possible to combine a narrow view of what counts as a source of a constraint with a broad view of what types of obstacle count as unfreedom-generating constraints, or vice versa. As a result, it is not clear that theorists who are normally placed in the ‘negative’ camp need deny the existence of internal constraints on freedom (see Kramer 2003; Garnett 2007).