Never use “and/or” in legal drafting, particularly when describing an obligation. It has been correctly described as an “ugly legalism”; William Strunk, Jr., and E.B. White, in their classic, The Elements of Style, say and/or is “A device, or shortcut, that damages a sentence and often leads to confusion or ambiguity”. They are right.
Justice Fowler, more colorfully, described it as “that befuddling, nameless thing, that Janus-faced verbal monstrosity, neither word nor phrase, the child of a brain of someone too lazy or too dull to know what he did mean”. Judicial criticism of this device is justifiably common.
The legal usage authority Bryan A. Garner correctly observed that use of this device (it is not really a word) is harmful in legal writing because a bad-faith reader – actually any reader with a financial interest in how a document is read – can pick whichever meaning suits them, the and or the or.
These are not hypotheticals. We have seen this problem in settlement negotiations over contract disputes in the U.S. and Asia. We have seen the use of this device unnecessarily prolong negotiations. And we have seen it result in one party paying millions of dollars more than it would have had to pay if the clause had been properly drafted.
Unfortunately, this will not stop lazy and careless lawyers from using this device. But careful clients should carefully review their legal documents to ensure that that this “verbal monstrosity” does not make an unwanted appearance in their documents. The costs are too great.