 This seems to be a perfectly sensible piece of advice. (1) appears to imply that it is optional that you attend—that you can attend and that you can fail to attend. The latter two uses of “can” express permissibility. Yet “ought” is routinely the reading given for deontic necessity in deontic logic (and in ethical theory), and then “permissibility” is routinely presented as its dual. However, if we symbolize (1) above accordingly, we get,