 Can we use the truth-functional understanding of “if” to propose that the consequent of any conditional (in (i), the consequent is “I used the key”) specifies a necessary condition for the truth of the antecedent (in (i), “I opened the door”)? Many logic and critical thinking texts use just such an approach, and for convenience it can be called “the standard theory” (see Blumberg 1976, pp. 133–4, Hintikka and Bachman 1991, p. 328, Moore and Parker 2009, 310–11, and Southworth and Swoyer 2020, ch. 3.2 for examples of this approach).