Such as is ambiguous—it might be unclear whether the clause it introduces serves to reduce the scope of the class represented by the preceding noun. This can result in contract disputes.
Consider the following sentence:
Richard collects books about painters such as Botticelli and Donatello.
Given the general nature of the class in question (painters) and the narrowness of the items in the such as phrase (two Italian painters of the early Renaissance), the reasonable reader would assume that Richard doesn’t collect books about all painters but instead collects books about painters comparable to those listed. In other words, the such as phrase reduces the scope of the noun painters—it’s acting like a restrictive clause. (For more about restrictive and nonrestrictive clauses, see this February 2007 post.)
The alternative would be for the nouns in the such as phrase simply to constitute examples of the class represented by the preceding noun. That would result in the such as phrase acting like a nonrestrictive clause. With respect to the sample sentence above, that could be accomplished either by narrowing the class represented by the preceding noun (see the first example below) or by including a broader range of nouns in the such as phrase (see the second example below):
Richard collects books about Renaissance painters, such as Botticelli and Donatello.
Richard collects books about painters, such as Botticelli, Edward Hopper, J.M.W. Turner, and Andy Warhol.
Placing a comma before the such as phrase, as in the two preceding examples, would help make the such as phrase nonrestrictive.
Nonrestrictive use of a such as phrase only makes sense if the meaning or scope of the class represented by the preceding noun might otherwise be unclear to the reader. That’s why the last of the above examples is rather ludicrous.
But a bigger problem is that a reader might be uncertain whether a given such as phrase is intended to be restrictive or nonrestrictive. For example, it might have been intended that the such as phrase in the second of the three above examples be restrictive—maybe the meaning sought to be conveyed is not that Richard collects books about all Renaissance painters but instead that he collects books about Italian painters of the early Renaissance. It would be rash to rely on a comma to ensure that a given such as phrase is read as being nonrestrictive.
For an example of a contract dispute caused by confusion regarding a such as phrase, see Lawler Mfg. v. Bradley Corp., No. 2007‑1533, 2008 U.S. App. LEXIS 11275 (Fed. Cir. May 27, 2008). (A big thank you to reader Mike Wokasch for telling me about Patently-O’s post about this case.) The contract in question specified that a given patent royalty rate applied “[i]f a Licensed Unit is invoiced or shipped in combination in another product such as an emergency shower or eyewash.” The question before the court was whether the such as phrase reduced the scope of the noun in question, “product”—in other words, whether the such as phrase was restrictive or nonrestrictive. The court reversed the lower court, holding that the such as phrase was restrictive—that the royalty rate in question didn’t apply to all products but only to products similar to those included in the such as phrase.
Given the general nature of the preceding noun (products), the narrowness of the nouns included in the such as phrase, and the absence of a comma before such as, the court’s holding was a reasonable one—the language at issue resembles the first of the three examples above.
But the contract language was sufficiently confusing that not only did it give rise to protracted litigation, it also prompted a dissent on the part of one Federal Circuit judge, who was of the view that the such as phrase was nonrestrictive.
Given the potential for confusion, don’t use such as. Instead, be precise in describing the class in question. If there’s any risk of uncertainty as to the boundaries of the class, resolve that uncertainty using including in the manner recommended in this April 2007 post. And whatever you do, don’t list for the heck of it obvious members of a class; see this post and this post about needless elaboration.