Final answer:
If John is locked in a room, he lacks free will in the matter of staying or leaving according to van Inwagen's perspective.
Step-by-step explanation:
In the context of van Inwagen's view, if John is locked in a room, it would be true to say that he lacks free will in the matter of staying or leaving. According to van Inwagen, free will is incompatible with determinism, which asserts that every event, including human actions, is caused by prior events and circumstances. If John is locked in a room, his ability to choose to stay or leave is restricted by the external circumstance of being locked in, thus limiting his exercise of free will. However, it is important to note that this statement is from van Inwagen's perspective and there are other philosophical perspectives that may offer different interpretations of free will.