The logical status of brain death criteria

This article is an attempt to clarify a confusion in the brain death literature between logical sufficiency/necessity and natural sufficiency/necessity. We focus on arguments that draw conclusions regarding empirical matters of fact from conceptual or ontological definitions. Specifically, we critically analyze arguments by Tom Tomlinson and Michael B. Green and Daniel Wikler, which, respectively, confuse logical and natural sufficiency and logical and natural necessity. Our own conclusion is that it is especially important in discussing the brain death issue to observe the distinction between logical and natural sufficiency/necessity in a strict fashion.