Here are my latest thoughts on an interesting categories-of-contract-language wrinkle discussed in MSCD 2.155–156:
You can express prohibition by means of an exception to language of discretion, but doing so could be a source of confusion, depending on how you do it. Consider the following: Widgetco may sell one or more of the Vehicles except the 1965 Ford Mustang. As a matter of pure logic, it could be argued that the exception excludes that vehicle from the scope of Widgetco’s discretion but does no more—in other words, the provision is otherwise silent regarding that vehicle, so Widgetco could sell the Ford Mustang without breaching the obligation. That’s a weak argument, as what The Cambridge Grammar of the English Language refers to as “the expectation of relevance” strongly suggests that the intention was to have the exception be equivalent to language of prohibition. But to avoid any chance of a dispute over meaning, it would be best to have the provision read as follows: Widgetco may sell one or more of the Vehicles, except that it shall not sell the 1965 Ford Mustang.
Expressing prohibition by means of an exception to language of obligation raises the same issue. If the above example were instead to read Widgetco shall sell all Vehicles except the 1965 Ford Mustang, as a matter of pure logic it could be argued that the exception excludes that vehicle from the scope of Widgetco’s obligation but does no more, so Widgetco could sell the Ford Mustang without breaching the obligation. In this case, too, that’s a weak argument, as the expectation of relevance strongly suggests that the intention was to have the exception be equivalent to language of prohibition. But to avoid any chance of a dispute over meaning, it would be best to have the provision read as suggested at the end of the paragraph above.
