The legal regulation of marijuana is in a state of flux in the United States. During the past dozen or so years, 18 states and the District of Columbia have passed measures permitting the use of marijuana for medical purposes. In the fall of 2012, two states — Colorado and Washington — went a step further and decriminalized entirely possession of less than an ounce of the drug. However, under federal law, marijuana remains a Schedule I narcotic; its manufacture and sale remain punishable by up to life in prison.

The contradictory legal status of marijuana in these states makes it difficult for individuals and businesses to conform their behavior to the law. It also creates particular legal and ethical quandaries for lawyers. Because growing and selling marijuana are serious violations of federal law, an attorney engaged by a marijuana business is necessarily putting herself at risk.

Under a literal reading of both criminal law and the Model Rules of Professional Conduct, attorneys are barred from knowingly assisting the criminal conduct of a client, and therefore prohibited from providing most kinds of legal assistance to a marijuana business. It would seem that any legal advice knowingly given to those working in the marijuana industry would expose an attorney to criminal sanction and to professional discipline as well.

Such a literal reading, however, would have serious negative repercussions in those states that have decriminalized marijuana. First, without the participation of attorneys, state policies regarding legalization or decriminalization would be frustrated. Because lawyers are often essential to implementing policy changes, law reform without the participation of lawyers will remain an unrealized promise.

Second, in a highly regulated society, conforming one’s conduct to the law often requires access to lawyers. Without their guidance, lay marijuana clients will be unable to ascertain the meaning and application of conflicting federal and state laws. Denied information, they would be unable to decide how to exercise their autonomy and conduct themselves under the law.

Last, such a strict reading would have a troubling impact on access to the law. Clients who lack legal knowledge will be unable to pursue their marijuana objectives, while more sophisticated clients may be able to engage in the same conduct without the assistance of lawyers. Moreover, some marijuana clients may be powerful enough to get lawyers to assume the risk of representing them, resulting in further inequalities of access. In other words, better educated and more affluent clients would likely fare better than others.

To avoid these problems, we look to the law of accomplice and co-conspirator liability for a solution. Most states today require that, for one to be found guilty as an accomplice, he or she must not merely knowingly aid another in the commission of an offense, but must form the actual intent to do so. This distinction between knowledge and intent is no idle, semantic one. This can be seen in the context of providers of lawful services who make them available to anyone who can pay. The gas station that sells gas to arsonists and drivers alike, or the website that accepts ads from prostitutes and gardeners alike, should not generally be held liable when the services are misused. This is true even when the provider knows that some of her clients are using her services for nefarious purposes.

The rationale for an intent requirement for criminal liability is grounded in part in respect for American individualism. The concern is that a knowledge standard would turn every merchant into his brother’s keeper, requiring each to inquire into his client’s motives and plans. Under an intent standard, by contrast, a merchant is generally protected from prosecution as an accomplice so long as she provides the same service at the same price to all clients, regardless of their plans for her services.

The intent requirement in accomplice and co-conspirator liability law provides a profoundly more sensible reading of the Model Rules for Professional Conduct. So long as lawyers merely know about — but do not intend to aid — marijuana clients’ violations of federal law, and so long as attorneys provide the same services to marijuana clients as they do to other clients, they violate neither their ethical obligations nor the prohibitions of the criminal law.

This reading generally permits lawyers to defend marijuana clients charged with violations of the Controlled Substances Act, to serve as lobbyists in challenging federal law, and to advise clients about state and federal marijuana law. Lawyers may also help marijuana clients with compliance work, negotiate leases for real estate space and advise clients about employment matters.

The lawful representation of marijuana clients is not without limits, however. When lawyers’ interests become directly aligned with those of their clients — when they have a stake in their clients’ business, for example, or when they charge a higher rate for those they know to be acting in violation of the law — it is reasonable to conclude they intend their clients’ illegal acts.

We are not calling for a general license to lawlessness. Our reading should only apply to minor criminal offenses, such as violating the Controlled Substances Act and only in states that have legalized conduct that the federal government has prohibited.

Sam Kamin is a professor of law and director of the Constitutional Rights and Remedies Program at the University of Denver Sturm College of Law. Eli Wald is the Charles W. Delaney Jr. professor of law at the school. A longer version of this piece, "Marijuana Lawyers: Outlaws or Crusaders?," 91 Or. L. Rev. 869 (2013), is forthcoming this April.