Should memos and briefs be written in plain English?
No, except in rare circumstances.

Memos are intended for lawyers, typically senior lawyers knowledgeable about the law. Briefs are intended for judges and their clerks and for opposing counsel—all lawyers. Documents intended for lawyers do not need to be written in plain English.

Granted, some plain-English principles work well in memos and briefs, and we all need to improve our analytical legal writing. But as a general principle, memos and briefs do not need to be written in plain English.

I wrote a series of posts about whether plain English–by which I mean “true” plain English as I define it–is right for transactional drafting. That series begins here. My conclusion was that true plain English, which I define as legal writing intended for nonlawyers, is not right for many transaction documents because they are not meant to be read and understood by nonlawyers.

Here’s what I think about plain English in memos and briefs.

The audience for analytical legal writing
All legal writing should be appropriate for its audience—it should speak to the reader in words, sentences, and forms the intended reader can understand. Thus, practitioner analytical legal writing—primarily objective memos and persuasive briefs—should be appropriate for their audiences: the supervisor who assigned the memo, the judges and clerks who will read the brief, and so on.

It is rare for the primary audience for a memo or brief to be a nonlawyer. Yes, it is conceivable that nonlawyer clients will want to read a memo or brief prepared on their behalf. It is conceivable that a memo or brief relates to a matter of public interest and that nonlawyers will want to read it. But neither situation is typical.

So when we talk about plain-English legal writing, we are usually not talking about memos and briefs. Instead, we’re talking about consumer transactions in which one or both of the parties is a nonlawyer.