  Harm arising from factors beyond one’s control is also central to why needs matter, when they do, on David Wiggins’s account (1987, 1998). Wiggins develops these ideas and introduces various terms to reflect central features of the concept. There is the gravity of the harm that would ensue if the need is not met (‘badness’), which is different from the urgency to prevent harm from ensuing. Needs may be entrenched when they are inflexible to modification, or substitutable when they are not. A need is basic if it results from a law of nature, an unalterable and invariable environmental fact, or a fact about human constitution. Using this terminology, Wiggins defines vital needs as ones that are bad in a way that is entrenched and scarcely substitutable, and it is these vital needs that matter morally according to him.