There’s an obvious contradiction: we expect people to behave consistently with what they say in a meaningful way. If I say, “I’m a vegetarian,” I’m not just making a factual claim, I’m also suggesting something about how I behave and what others can expect from me. That’s what philosophers and linguists often call a commitment: a kind of social obligation that a speaker takes on when they say something. This isn’t commitment in an everyday sense of dedication to a cause or loyalty to a partner, this is about what we ‘owe’ each other when we talk.

Commitments like this aren’t just about truth. They’re normative, meaning adherence to certain expectations about how we should behave when we communicate. If I say “I’m a vegetarian. I eat a lot of meat,” I defy the expectation created by my first statement. The problem isn’t just the inconsistency, it’s how I, the speaker, have chosen to present it.

So, conversation is about more than just trading facts. We also share and shape expectations and responsibilities. We undertake commitments for ourselves and even for others when we speak. These commitments are everywhere in our daily communication: we take them on, we interpret them, we might even go to lengths to avoid them. And yet, language scientists still don’t have a clear understanding of how this works.

That’s where some fresh new research comes in. In the Radboud University Philosophy Department, Harriet Yates, Corien Bary, Bob van Tiel, and Peter de Swart are designing methods to measure commitment directly, so we can figure out what actually happens in conversation, and what a good theory of commitment needs to explain.

The power of a frown

How do you study something as abstract as commitment?

For that, we look at tiny muscle movements in the face, often too subtle to notice. By placing electrodes on participants’ faces to pick up the small electrical currents that are generated when a facial muscle moves, we can track a participant’s micro-expressions as they read short conversational exchanges.

Here’s an example. Imagine Janice and Frank are talking about their friend. Janice says: “Tom is a vegetarian. He eats a lot of meat.”

If you’re like most people, you might feel a moment of confusion, a little suspicion, or even indignation. Something is off. That reaction shows up in people’s faces, especially in the muscle just above the inner eyebrow, which is linked to frowning. This muscle becomes active when you have a negative response towards something you see or hear, even fleetingly and unconsciously. We’ve found that this muscle becomes active as the second line is read, the moment at which you realize the speaker is contradicting their own prior statement.

This spike in activity tells us that the listener has picked up on a conflict between the first commitment made and the contradictory information which came after. Expectations have been broken and the commitment has been violated.

These findings hint at something powerful: we can detect and measure the dynamics of conversational commitment using subtle physical cues, even before anyone says something is wrong.

What else can we learn from frowns?

So far, our work has focused on simple factual contradictions; cases where a speaker says one thing, and then immediately undermines it with new information. But commitment goes far beyond these kinds of clear-cut cases.

What about things we might say on behalf of someone else? Does the way we present something someone else has said affect how committed we seem to be? For instance, is there a difference between saying, “I hear that Tom is a vegetarian,” and, “Tom is a vegetarian, I hear”? Both use what philosophers and linguists call an evidential marker, a phrase that softens the claim and signals that the speaker is relying on secondhand information. But do listeners interpret them in the same way? These kinds of subtle differences can shape how our commitments are perceived.

Here’s another question: might a listener unwittingly become committed to what’s said just by staying silent? If someone says, “Tom is a vegetarian,” and you don’t respond, you might not feel particularly involved or responsible. But what if they had said something offensive, like using a slur to describe Tom? In that moment, your silence might be taken as tacit endorsement. Do you feel a need to object or distance yourself?

Further questions are connected to this: can people only be held responsible for what they explicitly say? Or also for what they suggest, imply, or allow others to assume? Even small responses, like a nod or a quick “mm-hmm,” could signal agreement or alignment with a shared commitment. These conversational cues, verbal and nonverbal alike, help create the shared landscape of commitments between speakers.

Our long-term goal is to implement facial measurements to study these more subtle dynamics, combining insights from philosophy and linguistics with real-time physiological data. We want to better understand the link between what people say and what they’re understood to be committed to.

It’s an exciting direction for the study of language; one that opens up new ways of thinking about what we owe each other in everyday conversation.

Credits

• Writer: Harriet Yates

• Editor: Anna Mai

• Dutch translation: Lieke Herraets

• German translation: Carmen Ramoser