 One way to tackle this would be to treat or in  (18)  as a case of intensional disjunction. This solution however would fail to account for a characteristic aspect of the interpretation of disjunctive imperatives which arguably explains the failure of addition in these cases, namely their choice offering potential. The most natural interpretation of disjunctive imperatives is as one presenting a choice between different actions:  (18)  implies that you may post the letter and you may burn it (a free choice inference). Imperative  (17)  then cannot imply  (18)  otherwise when told the former one would be justified in burning the letter rather than posting it (e.g., Mastop 2005; Aloni 2007; Aloni and Ciardelli 2013). More on free choice in  section 6.