Massachusetts Rules of Professional Conduct Rule 3.1: Meritorious Claims and Contentions
A lawyer shall not bring or defend a proceeding, or assert or controvert an issue therein, unless there is a basis for doing so that is not frivolous, which includes a good faith argument for an extension, modification, or reversal of existing law. A lawyer for the defendant in a criminal proceeding, or the respondent in a proceeding that could result in incarceration, may nevertheless so defend the proceeding as to require that every element of the case be established.
Adopted June 9, 1997, effective January 1, 1998.
 The advocate has a duty to use legal procedure for the fullest benefit of the client's cause, but also a duty not to abuse legal procedure. The law, both procedural and substantive, establishes the limits within which an advocate may proceed. However, the law is not always clear and never is static. Accordingly, in determining the proper scope of advocacy, account must be taken of the law's ambiguities and potential for change.
 The filing of an action or defense or similar action taken for a client is not frivolous merely because the facts have not first been fully substantiated or because the lawyer expects to develop vital evidence only by discovery. Such action is not frivolous even though the lawyer believes that the client's position ultimately will not prevail. The action is frivolous, however, if the client desires to have the action taken primarily for the purpose of harassing or maliciously injuring a person, or, if the lawyer is unable either to make a good faith argument on the merits of the action taken or to support the action taken by a good faith argument for an extension, modification or reversal of existing law.
 The principle underlying the provision that a criminal defense lawyer may put the prosecution to its proof in all circumstances often will have equal application to proceedings in which the involuntary commitment of a client is in issue. The option granted to a criminal defense lawyer to defend the proceeding so as to require proof of every element of a crime does not impose an obligation to do so. Sound judgment and reasonable trial tactics may reasonably indicate a different course.
Corresponding ABA Model Rule. Identical to Model Rule 3.1.
Corresponding Former Massachusetts Rule. DR 7-102 (A)(1-2), DR 7-106.