Filler words like “um,” “uh,” “like,” and “you know” are not mistakes. They serve real cognitive and social functions in conversation, helping your brain plan speech in real time while signaling useful information to the person listening. Far from being verbal garbage, these tiny sounds are built into the mechanics of how humans communicate across every known language.
Your Brain Needs Processing Time
Speaking is one of the most cognitively demanding things you do. You’re selecting words, assembling grammar, planning what comes next, monitoring what you’ve already said, and reading your listener’s reactions, all within fractions of a second. Filler words buy your brain the time it needs to keep this process running smoothly without falling silent.
Brain imaging research confirms this. When people produce fillers like “uh” or “um,” areas of the brain involved in complex thinking (called association cortex) show significantly more activity than when producing ordinary words. This suggests fillers aren’t lazy speech. They’re a byproduct of your brain doing heavy cognitive work behind the scenes, searching for the right word or restructuring a sentence before you finish saying it.
“Uh” and “Um” Mean Different Things
These two fillers aren’t interchangeable. Research from Stanford’s Graduate School of Business found that “uh” tends to precede shorter pauses, while “um” comes before longer delays. In practice, this means your brain is sending a signal to the listener: “uh” communicates something like “hold on, I’ll be right back,” while “um” says “I need a moment to think through something more complex.” This distinction happens automatically. You’re rarely choosing between them consciously, but listeners pick up on the difference and adjust their expectations for how long they’ll need to wait.
Fillers Help Listeners, Too
Filler words don’t just help the speaker. They actively benefit the person listening. When you hear someone say “um” or “uh,” your brain gets a heads-up that new or unusual information is likely coming next. This allows you to pay closer attention and prepare to process something unexpected, which improves comprehension rather than hurting it.
Studies on conversation between native English speakers consistently show that fillers support rather than impede understanding. Even for people listening in a second language, fillers don’t necessarily cause comprehension problems and may actually help by giving extra processing time. The brief pause that follows a filler lets both speaker and listener sync up before the conversation moves forward.
Holding Your Turn in Conversation
Conversations follow invisible rules about when it’s your turn to speak. Silence is one of the strongest signals that you’re done talking, which means other people may jump in if you go quiet for even a second. Fillers solve this problem. Saying “um” or “uh” tells the other person you’re not finished yet. You’re still forming your thought, and you’d like to keep the floor. Without fillers, conversations would be full of awkward interruptions and false starts as people mistakenly assumed the speaker was done.
Every Language Has Its Own Fillers
Filler words are universal. Every studied language has them, though the specific sounds and words vary. In French, the most common filler is “euh.” Arabic speakers use “yaʿni” (meaning “means”). In Spanish, “este” (literally “this”) fills the same role as English “um.” Russian has an extensive collection, including “ну” (nu, roughly “well”) and “значит” (značit, “I mean”). Czech even has two terms for fillers: “word cotton” and “parasitic expressions.”
The sounds change from language to language, but the function stays the same. Every language needs a way for speakers to hold their place, signal thinking, and give listeners time to prepare. This consistency across unrelated languages suggests filler words aren’t a cultural habit. They’re a fundamental feature of how human speech works.
Who Uses Fillers Most
A study published in the Journal of Language and Social Psychology found that basic fillers like “uh” and “um” occur at roughly equal rates regardless of gender or age. Everyone uses them, and everyone uses them at similar frequencies. Where differences appear is with discourse markers, words like “like,” “you know,” and “I mean.” These tend to be more common among women, younger speakers, and people who score higher on measures of conscientiousness. The conscientiousness finding is counterintuitive: people who are more thoughtful and careful in their personality actually use more of these words, possibly because they’re working harder to make sure their listener follows along.
When Fillers Become a Problem
Fillers serve a purpose, but overusing them can backfire. Research on scientific presentations found that excessive filler use reduces a speaker’s perceived credibility and makes it harder for the audience to follow the message. The key word is “excessive.” A natural sprinkling of “um” and “uh” in conversation is expected and even helpful. But when fillers dominate a formal presentation, listeners start focusing on the fillers themselves rather than the content.
The difference comes down to context. In casual conversation, fillers are part of the fabric of normal speech. In prepared remarks, a high filler rate can suggest the speaker hasn’t organized their thoughts. This is why public speaking coaches emphasize reducing fillers: not because they’re inherently bad, but because audiences in formal settings interpret them differently than in everyday talk.
If you want to use fewer fillers in presentations, the most effective approach is simply becoming more familiar with your material. Fillers spike when cognitive load is high. The less you have to think about what comes next, the fewer fillers your brain needs to produce. Pausing silently instead of filling the gap takes practice, but it actually makes you sound more confident to an audience than rushing to fill every moment of silence with sound.