Between California’s megafires and the troubling extremist talk of recent elections, it’s a scary time no matter where you’re from. Meanwhile, the scariest news of all according to the latest U.N. I.P.C.C. report, that we have only a scant twelve years left to limit carbon emissions before we’re toast, has registered barely a whimper from the general public, despite the fairly conservative science-based consensus and careful communication behind it. Gravity is not just a good idea, it’s the law, as the joke goes. But scientists often seem to have trouble conveying the true gravity of things to the general public. Why?

The answer is not simple—these are complex issues. We are often distracted and motivated to act by the fiery language of populism but somehow ignore urgent information that could profoundly affect millions of lives when reported by scientists. Populists, of course, don’t arise in a vacuum, they need the right social context to gain traction. Politicians also happen to be quite good at clever rhetoric and repetitive messaging. Science has the rough end of the stick with the need for obscure jargon that’s harder for the lay person to understand. Scientists are just not as expert at telling stories the way people need to hear them. What many are looking for right now, during difficult times, is simple certainty, not nuance. This is reflected in the kind of direct, simple-to-understand language that the mass of people are drawn to. It’s also exactly the kind of language that conscientious scientists don’t tend to use.

As well as all these factors at play, it’s interesting that it can take just a simple element of grammar, boiled down, to make the difference between language that is powerful, and language that seems more uncertain—and perhaps even unbelievable: the boring old modal verb.

You might think nothing can be more grammatically dull and unremarkable than the closed set of function words we call modal verbs, like can, may, must, will, shall and more secondary modal verbs like could, might, ought to, would and should. But using them can have an outsized effect on how information is received by others, and subsequently even how we judge the speaker, their credibility and competence, without actually changing the content itself. Rather than being well-behaved classroom monitors helping the main verbs of a sentence, they are in fact linguistic rebels with an attitude problem.

Modals are weird verbs, syntactically defective in that they don’t inflect like regular verbs, and their very presence essentially messes up simple, direct statements by introducing very confused human feelings of uncertainty, possibility, obligation, permission, and ability into the mix.

Compare a sentence like “she’s the murderer” to “she must be the murderer” or “she might be the murderer.” The first is an ordinary declarative, that could be true or false but sounds objective. In the second and third, the speaker suddenly breaks the fourth wall and intrudes into the statement with their own uncertain beliefs (such as “I’ve deduced from other evidence she’s the murderer” or “I think it’s likely she’s the murderer”), even though the content hasn’t really changed. The presence of modal verbs such as “must” and “might” suddenly injects the speaker and their imperfect judgements into an objective statement, adding a certain kind of nuance, making them seemingly weaker and more tentative, opening it up for further questions. It makes it clearer that what seemed at first to be an objective statement is in fact from the point of view of the speaker.

But it gets worse. Not only do modals make declaratives sound less sure of themselves, they are also often semantically ambiguous, which messes up how you might read them. For example:

1. You must be very careful (i.e. you are required to be careful).
2. You must be very careless (i.e. you obviously are careless).
3. You must be very careful since you are able to paint such delicate pictures (i.e. you obviously are careful).
4. You must be very careless so that we can scare the guests off once and for all (i.e. you are required to be careless).

In these examples, the interpretation of “must” can only really be resolved by the context of the utterance itself, as Alex Klinge points out, rather than depending on just the lexical semantics of the word. (And how are we to understand an utterance like “you must try some of this delicious cake!” which pretends to be a requirement but isn’t really).

Modals can have multiple meanings, ambiguous readings (depending on context) and can even overlap with each other to mean the same thing in speech. Take the infamous grammar rule that can I is for asking about ability while may I is for asking permission. In common practice the two overlap and can (or may) mean the same thing. As a result of these semantic shifts over time, linguists have been confused about how to adequately categorize them into their core meanings, especially as in pragmatic communication they can often behave in messy, complex ways. This can certainly add to the general uncertainty and weakness that utterances with modal verbs are received than those without.

Declaratives without modals (or other linguistic hedges such as “I think,” “possibly,” etc.) have this straightforward objective power, even if the content is untrue. Compare sentences like “criminals have invaded our neighborhoods” vs. “the devastating floods that may have resulted in hundreds of deaths could have been due to climate change.” The presence of modals introduces nuance and opens up discussion. Depending on the modal verb used, the speaker can choose to convey varying degrees of certainty, for example the modal verb “will” as in “an average global temperature rise of two degrees celsius will result in higher death rates” has often been assessed by researchers as having the highest certainty, while a modal verb like “might” sounds much less sure.

The register of populist politics is definitive, repetitive, memorable messaging. Your typical politician or civil servant, however, may use longer, obscurer constructions with hedging to avoid being challenged on certain claims. A good example is the elegantly manipulative politician Frances Urquhart’s classic line from House of Cards, “you might very well think that, I couldn’t possibly comment,” chock full of modal verbs with a side helping of plausible deniability. We’re used to thinking that someone using this kind of language is probably untrustworthy, with something to hide. In fact, some studies have shown that when people use linguistic hedging, like modal verbs, to temper how sure they are of something, they can be perceived as less credible, competent and authoritative, and more powerless in formal environments like the courtroom.

Despite this, researchers have noted that scientific and academic writing often contains quite a lot of linguistic hedging, such as the use of modal verbs, in the very environment that seems to call for powerful conviction and clarity. Though style and grammar guides sometimes advise scientists to avoid using modal verbs in their work to reduce ambiguity and misinterpretations of what are otherwise evidence-based and often precise findings, scientists and academics can’t seem to help but use them liberally. Some studies have even cautioned that modal verbs and other hedges may cause other researchers to misreport results when citing them.

So if modal verbs are just going to introduce ambiguity and obfuscation, and make people assume you don’t know what you’re talking about, or worse, that you have something to hide, why even use them?

To many, real language is about saying what you mean. That means using the literal, logical, lexical meanings of words. Direct speech and plain speaking is often valued in a way that indirect speech is not, regardless of whether the content is true. I’ve heard from some frustrated folk recently who view indirect speech as a kind of passive aggressive behavior designed to manipulate. Yet indirect speech acts, such as someone answering “I’m too tired” to refuse an invitation, or a superior saying “That’ll be all” to a subordinate as an imperative to leave the room, are very common ways we use to express social politeness and face saving as we negotiate power relationships. As much as we want to assume otherwise, language (as well as science) in practice is messy and often not logical when it comes to using spoken language.

It’s important to understand that language is not just about the bare content of what we say, but also the interpersonal and social functions of how we say it. As an example, I once said “I might go now,” meaning I had every intention of leaving and an American friend immediately joked “Might you? Don’t you know if you are?”

This dialectal difference is important, especially as modal usage has changed greatly over time. Although an American might read the sentence as oddly weak and unsure, a British or Australian English speaker understands that, in a certain context, there’s another subtle nuance here: an indirect form of cooperative politeness. As in, “I intend to leave now… unless you have some reason why I shouldn’t.” This is also true of Appalachian English’s multiple modal constructions, which Margaret Mishoe and Michael Montgomery show are often used when the social situation calls for negotiating politeness, indirectness and saving face, as in this exchange:

[Customer:] […] the car is driving fine. I’m just a little concerned and I thought you MIGHT COULD know right off what it is […].

[Repairman:] […] We MIGHT COULD’VE overlooked something.

The interpersonal aspect of how we use things like indirect speech acts, hedges, and modal verbs in some ways is more important than the literal lexical meaning itself. Crucially, modals and other hedges and indirect speech are commonly used by all of us to indicate a kind of cooperative politeness and reduce face threatening acts (as well as for other purposes, such as when one is unsure or trying to avoid saying something). Scientists increasingly understand, perhaps in a way that the public doesn’t yet, that using hedging language is often necessary to conscientiously convey more accurate degrees of certainty. This doesn’t mean, however, that their findings should be dismissed as not authoritative. That allows for scholars to be more collegial and circumspect in presenting work, which may often challenge and pick apart the previous work of colleagues. Modal verbs used in hedging open up debate, and allow researchers to be more measured about the true certainty of their findings and conjectures, as few things in science are a hundred percent absolute.

So this is not to say that scientists presenting their work should aim to speak in short, definitive statements, because stating something as a fact doesn’t make it true. It’s good to be aware that linguistic hedging, even when it comes to your basic modal verb, may erroneously encourage the public to believe that an expert is unsure of what they’re talking about because of how this language is sometimes viewed in other environments such as politics and the courtroom… but it is exactly this careful and nuanced language of science that we should value and seek to understand.