Facial expressions are not just part of sign language, they are essential to its grammar. In American Sign Language and other signed languages, specific facial movements function as question markers, negation, adjectives, and even verb tenses. Without them, most signed sentences would be incomplete or incomprehensible, much like speaking English without intonation or word order.
Linguists call these movements “non-manual markers,” a term that covers facial expressions, head positions, and body postures that work alongside hand signs. They operate at every level of language structure, from individual words to full sentences. Thinking of facial expressions as optional emotional flavor is one of the most common misunderstandings about sign language. They carry specific, rule-governed meaning.
How Eyebrows Mark Question Types
One of the clearest examples of facial grammar is eyebrow position during questions. ASL has two distinct eyebrow rules depending on the type of question you’re asking.
For yes-or-no questions (“Are you hungry?” or “Did she leave?”), the signer raises their eyebrows on the final sign of the sentence. This brow raise is what tells the viewer it’s a question at all, since ASL doesn’t rearrange word order the way English does to form questions.
For open-ended questions using WHO, WHAT, WHEN, WHERE, HOW, HOW MANY, or WHY, the rule flips: eyebrows go down, and the brow furrows. Signing “WHAT YOUR NAME” with lowered brows asks someone’s name. Signing the same words with neutral eyebrows doesn’t read as a question. The facial expression isn’t decoration. It’s the grammatical equivalent of a question mark.
Mouth Shapes That Work Like Adjectives
ASL uses a system of mouth shapes, called mouth morphemes, that modify the meaning of hand signs the way adjectives and adverbs modify nouns and verbs in English. These are distinct from mouthing English words. They’re their own system with consistent rules.
- “MM” (lips pressed together): Conveys “moderately,” “normally,” “with ease.” Paired with a sign for driving, it means driving along comfortably.
- “OO” (small rounded mouth): Indicates something small, tiny, slow, or light. Used with a size-related sign, it specifies that the object is very small.
- “CHA” (mouth opens wide): Means very big, gigantic, very tall. Signing a description of a building while mouthing “CHA” tells the viewer it’s enormous.
- Puffed cheeks: Can mean fluffy, bubbly, or large depending on context.
- Puckered lips (“mmmm”): Indicates enjoyment, curiosity, or comfort. Paired with the sign for READ, it suggests someone is reading contentedly.
These mouth shapes are not improvised. Signers learn them as part of vocabulary, and using the wrong one changes the meaning of a sentence just as swapping “tiny” for “enormous” would in English.
Negation and Head Movement
To negate a statement in ASL, signers can use signs like NOT or NONE, but they can also negate an entire sentence simply by shaking their head while signing it. A head shake during “I LIKE COFFEE” turns it into “I don’t like coffee” without adding a single manual sign. This head shake is grammatical negation, not just an emotional gesture of disagreement.
Similarly, a technique called topicalization uses raised eyebrows and a slight head tilt to establish the topic of a sentence before commenting on it. This is roughly equivalent to saying “As for pizza, I love it” in English, where the raised brows during “PIZZA” set up what you’re about to discuss.
Linguistic Structure, Not Just Emotion
Thirty years of linguistic research have confirmed that facial expressions in sign languages function at every structural level. Some individual signs have an obligatory facial component as part of their base form, meaning the sign is incomplete without the face. At the sentence level, brow raises mark conditional clauses (“if” statements), and specific head positions distinguish between statements and commands.
This is a critical distinction: sign languages use both emotional facial expressions (smiling because you’re happy) and grammatical facial expressions (raising your brows because you’re signing an if-then statement). These are different systems. A signer can produce a grammatically “happy” sentence structure while conveying sad content, just as an English speaker can say something sarcastic with a flat tone. The grammar and the emotion operate on parallel tracks.
Differences Across Sign Languages
Not all sign languages use facial expressions in the same way. ASL and British Sign Language (BSL) are mutually unintelligible languages with different vocabularies, grammar, and conventions for non-manual signals. ASL relies heavily on facial expressions for grammatical functions like marking tense, while BSL leans more on body movements and handshapes to carry some of that same information. A raised eyebrow or pursed lip in ASL may carry a different meaning in BSL, or no specific meaning at all.
Both languages use non-manual signals, but the balance differs. ASL integrates facial grammar so deeply that learning to sign without it is like learning to write English without punctuation or capitalization. You might get your point across occasionally, but you’ll be misunderstood constantly. BSL uses facial expressions extensively too, but distributes some of that grammatical load across other channels like hand movement patterns and classifiers.
These differences reinforce the broader point: facial expressions in sign language are not universal, instinctive reactions. They are learned, language-specific grammar that varies from one signed language to another, just as spoken grammar varies between English, Mandarin, and Arabic.