Perhaps Chisholm was thinking that this puzzle could be solved by appeal to a system of deontic logic based on the notion of requirement. Maybe he thought that a good way to represent the sentences in question would be to say (a) that Smith had a non-overridden requirement to go to the aid of Jones; but that (b) that if Smith were going to go to the aid of Jones, then this fact would require that Smith notify Jones in advance; and furthermore (c) that if Smith were not going to go to the aid of Jones, then this fact would require that Smith not notify Jones in advance. Finally, there is the stipulation (d) that Smith is not going to go to the aid of Jones. This solution to Chisholm’s puzzle would be of greatest interest if it could be shown not only to provide a suitable semantical interpretation for the four cited sentences, but also to pave the way to a complete system of deontic logic adequate for the expression of statements of conditional obligation.