“Shall Not … Unless” Versus “May … Only If” (Updated!)

[Updated December 9, 2014]

One of the privileges of blogging is that it gives you the opportunity to talk utter BS without doing much damage. A case in point is this post, originally published on August 4, 2014.

To recap, the issue was whether one of the two following alternatives was preferable to the other:

Acme shall not sell the Shares unless Widgetco consents.

Acme may sell the Shares only if Widgetco consents.

In an August 6 update I opted for the version with shall not, saying that it avoids the uncertainty inherent in the version using may … only. Well, I’m here to tell you that that’s incorrect, in that both versions incorporate uncertainty.

In the version with shall not, the question is what category of contract language applies if Widgetco consents. Our old friend the expectation of relevance (more about that here) suggests that Acme may sell the Shares if Widgetco consents, but it’s conceivable that it might instead be obligated to sell the Shares if Widgetco consents.

And in the version with may … only, the expectation of relevance suggests that Acme may not sell the Shares if Widgetco doesn’t consent, but it’s conceivable that it might instead be obligated to sell the Shares if Widgetco doesn’t consent.

So in terms of uncertainty, there’s nothing to choose between the two. To eliminate that uncertainty you’d have to say the following:

Acme shall not sell the Shares, but it may sell the Shares if Widgetco consents.

(You could say instead Acme shall not sell the Shares unless Widgetco consents, in which case Acme may sell the Shares, but I have a slight preference for the version using except, as it’s shorter.)

Would I go to the trouble of eliminating the expectation of relevance? I think so, but I acknowledge that doing so would be pretty hard-core.

If you don’t want to eliminate the expectation of relevance, which of the two original options would I go for now? Still the version with shall not. The default position is that absent contract restrictions, one may do stuff, so it follows that it’s the prohibition that has teeth; I’d lead with it.

[Original August 4, 2015 Post]

Last week I saw this tweet by @lisasolomon:

That led to a discussion involving @CherylStephens and ProfJoeKimble: which is preferable, shall not … unless or may … only if:

Acme shall not sell the Shares unless Widgetco consents.

Acme may sell the Shares only if Widgetco consents.

My Twitter interlocutors all favor option two (language of limited discretion) over option one (language of prohibition with an exception), on the grounds that it’s easier to understand concepts that are expressed in the positive rather than the negative.

Although I haven’t yet had a chance to research that notion (Semantics and Comprehension, anyone?), it sounds sensible. But I wondered whether desirability of the action in question is a factor:

Acme shall not destroy the Equipment unless Widgetco consents.

Acme may destroy the Equipment only if Widgetco consents.

I think there’s something to be said for stating as a prohibition that which you really don’t want to happen. But I invite all you semantics ninjas to wade in on that.

I should also mention the ambiguity inherent in may … only. Consider the sentence Widgetco may sell only the 1965 Ford Mustang. Presumably the intended meaning is that the only vehicle that Widgetco is permitted to sell is the vehicle specified. But it could also mean that Widgetco may elect to sell only that car but would also be free to sell other cars instead of or in additional to the Ford Mustang, or not sell any cars. In other contexts, the more natural meaning is analogous to the latter meaning. (See MSCD 3.155–59.)

Those alternative meanings present themselves even if instead of being part of the subject only introduces a conditional clause, as in Acme may sell the Shares only if Widgetco consents. But the second possible meaning (consistent with the logic outlined in the previous paragraph) is so strained that I wouldn’t say that the alternative meanings give rise to ambiguity. So in this context, the ambiguity of may … only isn’t a factor.

[Updated August 6, 2014: Thank you all for a very enlightening exchange. I have made my decision; let’s call it “The Decision,” LeBron James-style.

Henceforth, I will aim to use—cue drum roll—shall not … unless.

It boiled down to choosing the lesser of two evils. One of the evils is the modest tax on comprehension that comes with expressing an idea in the negative rather than the positive. The other evil is the alternative meanings that come from using language of limited discretion. The expectation of relevance suggests that if Acme may destroy the Equipment only if Widgetco consents, then Acme may not otherwise destroy the Equipment. But as my linguistics buddies are fond of saying, that’s an implicature—it’s not the only meaning; see A. Wright Burke’s comment.

The odds of the alternative meanings associated with the may … only if version creating a problem are infinitessimal. But I prefer to train myself to spot ambiguity and eliminate it wherever possible, to increase the odds of my catching those instances that might well lead to dispute.

This isn’t my final word; I’ll have to refine my analysis for purposes of MSCD4, and I wouldn’t be astonished if I think of some new angles. Meanwhile, I expect proponents of may … only if to start rioting, flipping cars, and stuffing a lone cardboard-cutout image of me head-first in the nearest trash can.]

About the author

Ken Adams is the leading authority on how to say clearly whatever you want to say in a contract. He’s author of A Manual of Style for Contract Drafting, and he offers online and in-person training around the world. He’s also chief content officer of LegalSifter, Inc., a company that combines artificial intelligence and expertise to assist with review of contracts.

32 thoughts on ““Shall Not … Unless” Versus “May … Only If” (Updated!)”

  1. I think you’re right on both points. Framing the issue as positive or negative (which is much the same issue as allowing only with consent or allowing unless objection) should depend on what you want the default situation to be and what the exception is. This is not meaningless: choosing different words and structure to communicate the same meaning, but better, is good writing.

    So the issue is not a preference for positive language over negative language (and, as an aside, the research in applied behavioral analysis, used among other things to treat people with autism, supports the idea that positive language is better because people know what they should in fact do), but one about what the default scenario is. Which way will a court interpret the language? Is there a right subject to an exception, or a prohibition subject to consent? The option you choose may well change things like burden of proof, at least in terms of who will be expected to prove what, regardless of the technicalities of who sues whom.

    As for “may,” I’ve banished it in favor of “is entitled to,” with “is not entitled to” as a replacement for “may not.” I agree that the ambiguity of “has a right to” and “might do X” is not helpful.

    • Thanks for framing it that way.

      I don’t want to get off on a “may” tangent, but I’m sticking with “may.” Unless the benefits of change are clear-cut, I prefer not to recommend that people change established usages. It’s very unlikely that anyone would ever get into a fight over whether a given “may” grants discretion or means “might.” (Your challenge: find me an example of such a dispute!) And if you mean “might,” then use “might.”

  2. My three cents:

    (1) My apologies to Gandalf (“You shall not pass….”), but it’s better to get rid of the shall in #1. “Acme must not sell the Shares unless Widgetco consents.”

    — or —

    (2) Turn #2 into an if/then statement: “if Widgetco consents [to it], then Acme may destroy the Equipment.” [bracketed words optional].

    I’m not sure that any of the examples creates ambiguity, however. It’s plain that ACME must not sell the shares unless it first gets Widgetco’s consent to do so.

    (3) I disagree with Rick C. below who advocates striking “may” in favor of “is entitled to.” It’s two more words for the reader to process with no benefit.

    • I agree completely with your #3, and disagree completely with your #1, assuming Acme is a party to the contract. That violates the Prime Directive of disciplined verb use: “shall” imposes an obligation on a party to the contract (whether positive or negative). For *anybody or anything else* you use “must” or reconfigure the sentence to describe those things as conditions to some obligation or action of a party. A contract, after all, can only issue orders to its parties; all others may [i.e. are at liberty to] allow their attention to wander.

    • Regarding your first point, let’s not use every occasion to revisit “shall”! :-)

      Regarding your second point, yes, it’s perhaps better to place a short conditional clause at the beginning of the sentence; see MSCD 3.257. But crucially, you omitted the “only”; it’s essential. If you include the “only,” putting the conditional clause at the beginning of the sentence becomes more awkward. And as regards “then,” MSCD 3.251 says, “if the conditional clause is relatively short, adding ‘then’ to the matrix clause just adds a bit of dead weight to the sentence.”

      Regarding your third point, Rick’s suggestion does have a benefit, namely avoiding confusion over the two meanings of “may.” But as with so many drafting choices, it’s a matter of balancing the risk and the benefit.

      • I take every opportunity to make my must-not-shall point! ;)

        I’m not sure that “only” is necessary in #2. The context of the sentence suggests that the only condition precedent is Widgetco’s consent, so “only” is tautological—not essential—in both Lisa’s original example and your example.

        It’s arguable that the “then” in my example makes the one condition precedent unmistakably clear. But I’ll graciously concede that point. The “then” isn’t essential.

    • Matthew:

      I tend to follow Ken’s guidance on the use of must (and hence, must not). It is very useful to have shall (and shall not) focused on imposing a duty (or prohibition) on a party. That leave must (and must not) for ancillary uses, such as:
      1. when the person to perform the task is a person who is a non-party, like a court or arbitrator (see MSCD 3.106); and
      2. expressing conditions (see MSCD 3.263-3.269).
      The two constructions are sufficiently different that they are unlikely to be confused, allowing must (and must not) to serve double-duty. I particularly like the first one, since there is really no better alternative. You can re-write most conditions to avoid the word must (or must not), but they tend to get wordier.


  3. Ken:

    My theory is that, if anyone could argue something with a straight face, someone will. So, I prefer to avoid “may not” on the ground that some quasi-literate could argue that it meant “may decline to” (leaving it in their discretion) rather than shall not. Yes, I could avoid the circumstances in which that ambiguity is present, as you recommend in MSCD 3.115-3.159 and in your comments. But that’s extra work, so I prefer a rule that doesn’t require me to think as much to avoid ambiguity.


    • You know already that MSCD recommends using “shall not” instead of “may not.” So the alternative meanings of “may” come into play only for purposes of language of discretion, to the extent that one is worried about them (and I’m not).

  4. Not being a semantics ninja, I haven’t the vocabulary to work through the deep misgivings I have about language of discretion in general and the word “may” in particular, but I can say this: sometimes the expectation of relevance shaves away logically possible interpretations of a “may” construction, if “may” is understood to authorize doing or not doing a thing.

    For example, “Acme may destroy the equipment only if Widgetco consents.” [Without the discretion conferred by such consent, Acme *shall* destroy the equipment.]

    The bracketed sentence isn’t implicit in the sentence before it. But it highlights the point that when you say only that there’s no discretion to do or not do a thing (e.g., because a condition for such discretion is unmet), you haven’t said whether it is action or inaction that is therefore mandatory.

    A better example: “Crossing the border is discretionary only on weekends” (= “One *may* cross the border only on weekends”). Under that rule, is crossing the border on weekdays mandatory or forbidden?

    Since whether something is an action or an inaction depends on phrasing (“not going to school” vs. “skipping school”), it’s probably better to draft contracts using the prohibition subject to an exception rather than a grant of discretion subject to a condition.

  5. Version 1 is a contractual prohibition, breach of which entitles Widgetco to damages. Query whether Version 2 has the same contractual consequences.

    Both versions raise the issue of whether the implied covenant of good faith and fair dealing require Widgetco to be reasonable in exercising its discretion whether to grant consent. The answer varies depending on the governing law. Some states imply a reasonable exercise of discretion; others do not.

    Arguably, Widgetco is better off from a business perspective if the contract absolutely prohibits the destruction of the equipment and has no provision dealing with consent. The revised provision would not preclude the possibility of Acme destroying the equipment. It would change, however, how Acme obtained the right to do so.

    If the contract were drafted as an absolute prohibition, instead of seeking Widgetco’s consent, Acme would have to ask Widgetco to waive the prohibition. In either event, Acme must receive some piece of paper from Widgetco. But which piece of paper matters. With no contractual provision referring to the possibility of consent, Acme would have a much harder time arguing that Widgetco had impliedly agreed to be reasonable in deciding whether to waive the prohibition. What used to be an easy give in a negotiation (qualifying a prohibition with the right to seek consent) now requires more careful analysis.

    • Regarding your first point, my priority is semantics. There’s no reason why courts should treat one version differently from the other; in the absence of a clear indication that there’s a risk that they might do so, I’m not going to worry about that.

      Regarding the duty of good faith, it’s not relevant to the question I posed. I could have ended each version with “Widgetco paints its offices pink” or “the price of vanadium is over $25,000 per gram” or some other way that doesn’t involve good faith. In future writings on this issue, I’ll make a point of doing so.

      The same applies to your third point: I hadn’t intended to provide such an easy way out!

  6. Generally I would prefer the “shall not” construction for these kinds of purposes, for reasons given by others. However, if it was in the context of a provision that was already granting discretion, I feel it makes more sense to use “may”. For example:

    “Acme may sell any of Widgetco’s Equipment, except that it [may only sell any of Widgetco’s Equipment that is blue if….] [may not sell any of Widgetco’s Equipment that is blue unless…].”

    Using “shall not” in those cases probably does work, but it jars a little against the earlier use of “may” to grant discretion. Using “may” consistenty works better for setting out the full scope of a discretion.
    Of the two options I set out, I would probably prefer the latter – it’s more equivalent to the “shall not…” construction, and the “may not” ambiguity is not one that keeps me up at night (especially so in this context).

  7. I prefer “shall not…unless” rather than “may…only.” First, as a general matter, “may” can mean “is/are permitted to” (i.e., discretion) or “might possibly.” I know that context plays an role here, but I now use “is/are permitted to” to convey discretion rather than “may” And I use “might” to convey possibility. Second, as you note, “may…only” can result in ambiguity. Third, I agree with Tina that “shall not” does a better job of creating an obligation, which, if breached, will result in a breach of contract. Finally, as a general rule, I avoid creating rights out of thin air, i.e., I only use language of discretion as an exception to an express or implied prohibition in the contract or at law. Perhaps it’s because of my libertarian leanings, but I don’t want to tell someone what he or she (or it) has the “right to do” unless that right has been expressly or impliedly taken away from that person by law or by contract. Also, there is a danger that if you grant permission out of thin air, you imply a negative covenant. For example, if I “give you the right” to go to the movies on Monday, Tuesday, Wednesday, Thursday, Friday, and Saturday, there is an implication that you are prohibited from going on Sunday. While I understand that, depending upon the context, you can solve this with “may…only,” it feels awkward to do so; I would rather state the prohibition expressly.

    • I think you’re mixing two issues, namely (1) whether to use “shall not” or language of limited discretion and (2) how to express language of limited discretion.

      I won’t be joining you in using “is/are permitted to” and, necessarily, “will be permitted to” for “may.”

      Regarding Tina’s point, see my response to Tina.

      Language of discretion raises enough semantics issues without my finding some philosophical bone to pick with it. Indeed, the one point I agree with you on is the one expressed by A. Wright Burke: the expectation of relevance is still an issue in my example.

      • Yeah, I admittedly shoe-horned in my feelings about the use of “may.”

        Others may join me in the crusade against “may”…

        • You can reduce your word count with a quick definition of “may” as “to be permitted to” or whatever else you want it to mean.

          Ken is death on excess definitions and interpretive rules (the latter, what he and most people call “drafting conventions”), but I think they’re a wonderful way to economize. E.g., “duty” means “obligation”; “need not” means “is not required by this contract to.”

          My problems with language of discretion is apparently what Ken calls semantic or philosophical. WARNING: What follows is densely airy-fairy, if that’s possible.

          What is the essence of discretion?


          (1) A duty to choose and do one thing from a set of possibilities that includes doing nothing as a possibility. “The janitor may come in on weekends to unpack and shelve supplies.”

          (2) A duty to choose and do one thing from a set of possibilities that does not include doing nothing as a possibilities. “The contractor shall paint each house one of the following colors, at the contractor’s option: red, yellow, blue.”

          (3) A duty to choose more than one thing from a set of possibilities that includes doing nothing. “The guard may work on making mosaics during his breaks in the Break Activity Room, but shall include some red, yellow, and blue tiles in each such mosaic.” (Sorry for the stupid example.)

          (4) A duty to choose more than one thing from a set of possibilities that does not include doing nothing. “The contractor shall paint all 144 houses, but (a) shall paint each one no other color than red, yellow, or blue; (b) shall not paint any two adjacent houses the same color; and (c) shall paint 48 houses in each of the three colors.”

          These examples all cast “discretion” as some kind of duty or conditional duty. I wonder whether that makes sense.

          Does this example grant the Donor discretion or not? “In return for the Donation, the Museum shall admit the Donor to the Museum whenever it is open to the public without her paying the usual admission charge.”

          If that example confers discretion, it does so without using “may” or its variants.

          I have the intuitive feelings that (a) I’m in over my head; (b) this is well-trod ground for some kind of expert; (c) there’s no way that I will be reading books with titles like “Semantics and Comprehension.”

          Best of luck, Ken, with the 4th edition’s treatment of language of discretion.

          • I look forward to digesting it! But meanwhile, “semantic or philosophical”? First off, you imply that that’s something I said dismissively, but semantics are at the center of my world. As for “philosophical,” I’ll apply that to a discussion of whether Ayn Rand would approve of language of discretion, but I can’t imagine using it otherwise. I’m mortified. *sniffs*

  8. Not to be a but-insky, BUT couldn’t you shorten your new preferred language by replacing “except that it” with, well, “but”?

  9. Ken:

    A shorter version that might encounter less redlining:

    “Acme shall not sell the Shares, but may do so if Widgetco consents.”


    • Ken:

      A further thought. In NDA’s, the fundamental structure is a prohibition on use and disclosure, with loads of exceptions. (That fundamental structure is often obscured by bad drafting.) In NDA’s, I often use something like this:

      “Recipient shall not use or disclose the Confidential Information except as this agreement expressly permits. Recipient may use the Confidential Information to consider entering into a transaction with the Discloser. [etc.] Recipient may disclose the Confidential Information to its own employees who have legally enforcable duties not to further disclose it. [etc.]”

      The point is that, if you have more than one exception to a prohibition, you can simply ass “except as [whatever] expressly permits” to the end of the prohibition and put permissions into separate sentences. Then the language of each part is easy tio figure out using MSCD.


  10. There’s still some underbrush to be cleared away on this subject. I’m still wrestling with it and so speak tentatively.

    ‘Acme shall not sell the Shares unless Widgetco consents’ means the same as ‘Acme is prohibited from selling the Shares, but if Widgetco consents, Acme is not prohibited from selling the Shares’.

    Ken, you correctly note that merely stating the absence of a prohibition leaves a silence about whether the unprohibited action is allowed or required.

    Here we must distinguish between the logical point that what is not prohibited must be either allowed or required, and the linguistic near-certainty that what is said not to be prohibited is therefore allowed and not required.

    So any contract statement that amounts to ‘X is prohibited, but if Y consents, X is not prohibited’ clearly but implicitly means ‘If Y consents, X is allowed but not required’.

    You can very concisely make the implicit explicit by a formulation like ‘X is prohibited, but if Y consents, X is allowed’, but it sounds a bit strange.

    Whether that ‘fix’ is simple prudence or like wearing a tinfoil hat against mind rays from space is, I suppose, a judgment call. -Wright

  11. The ambiguity you point out is what happens when W consents — does A have a mandate to sell or the discretion to sell? I’m probably oversimplifying this, but here goes. The “shall not” formulation is a prohibition with an exception, and the sentence is simply silent on what happens if the exception applies. If A would be mandated to sell absent the prohibition, A is mandated to sell if W consents. (And I’d suggest that’s a bad use of the word “consent” because the effect is to give W the power to direct A to sell, not merely to acquiesce to something A wants to do.) Most likely, A has the discretion to sell absent the prohibition. . . otherwise, why would the prohibition be necessary? But either way, the silence should be filled by the context of the sentence. If it’s not already filled, and if that’s a problem, then fill it. Don’t leave it to chance.

    I don’t see that the “may . . . only if” formulation is very likely to create an ambiguity. It’s a grant of discretionary authority subject to a condition. If the condition is satisfied, the grant is effective. The satisfaction of the condition does not turn the grant of discretionary authority into a mandate. The ambiguity, if there is any, is what happens absent consent; again, that needs to be filled by the context. (Frankly, I don’t see much difference between “may . . . if” and “may . . . only if.” Or even “may. . . but only if.” In my view, the difference, if there is any, is merely one of emphasis that might help inform the reader as to the drafter’s intent. . . or might not.)

    Two points: 1. Brevity is good, but not if it creates ambiguity that may turn out to be a problem. If it does, use more words to eliminate it. 2. Don’t over analyze single sentences in isolation from their context. That’s not the way contracts are read. At least it’s not the way they should be read.

    • Mind if I add my 2 cents – I’m not a lawyer- I’m a buyer, who has experienced many attempts by contractors to creatively interpret contracts. I prefer not to imply that the contractor has a choice by using “may” nor to grant a contractor some arguable right by using “entitled to”. I also prefer to avoid opening a possibility at the beginning of a sentence and limiting it at the end of the sentence – since many contractors will only read the first half. Even though I might win in court, I’d rather contract performance was as expected.

  12. Why not be very clear about options and say: Acme shall not sell the Shares, but it may sell the Shares, if it so chooses, if Widgetco consents

  13. Why not just say “Widgetco has permission to sell the Ford Mustang and does not have permission to sell any other vehicles”


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