Which better reflects an individual’s intelligence: their spoken words or written words? Most people might initially think writing because that is how the most intelligent ideas are spread: in books. But, essentially, speaking is to writing as taking a test is to taking an open-book test. When writing, the “book” is every book ever—the entire internet: Google, Wikipedia, academic papers, etc. All of human knowledge is at your fingertips.
Writing is not necessarily a true reflection of one’s intelligence because, in a sense, it is cheating—you are able to copy the intelligence of others. Whereas when speaking, you have no cheat sheets. You are not able to look up facts and figures on the internet—all you know is what’s already in your brain. You have no outsourced knowledge from books or computers. Therefore, in a speaking debate, if one person sounds more intelligent on a certain topic, it is probably because they are. They hold more knowledge on the topic in their brain. Unless the speaker is merely more talented at rhetoric and persuasion and is able to use emotion to manipulate the audience into believing they are more knowledgeable than they truly are. Just as the speaker cannot look up facts, neither can the listeners verify claims.
On the other hand, intelligence is not just “what you know.” True intelligence is not how many facts one can memorize—it is one’s ability to think. An IQ test does not measure your knowledge of facts but your logical reasoning skills. The most intelligent are those that can take in the massive amounts of information in the world today (all of history, science, news, fake news, etc.) and reason through it logically to figure out what is true and what is false. True intelligence is not based on having read the most books, or being able to do the most complex math, or engineer the most advanced technology, or make the most money. True intelligence is the ability to best understand the truth of the world around you.
This is why philosophers (or certain generalist philosophers) are perhaps the most intelligent humans in the world. They do not focus on one area in life (such as quantum physics, or chemistry, or computer programming, or biology, or economics, or politics, or finance, or engineering). They do not devote their entire lives to one specialized subject to become the most knowledgeable person in their respective fields. Instead, philosophers study ALL those fields, though never in as much depth as the specialized experts. Generalist philosophers, through their reasoning skills, are able to understand the findings of every intellectual field without having to take part in producing any discoveries themselves. Society needs both generalists and specialists. One is not necessarily more intelligent than the other; they are different types of intelligence.
Generalist philosophers are not as knowledgeable about any one subject as the top experts in each field, but they have more broad knowledge than the specialists because they know more about more subjects. Obviously, not all philosophers study broadly, and not all generalists are equally skilled at logical reasoning. Some have biases and/or focus too much on philosophy itself—or the philosophy of philosophy. Some philosophers can get caught in the weeds rather than focusing on the root meaning of philosophy: “love of wisdom.” The true philosopher studies all current knowledge, and the most intelligent philosopher is the one who most wisely interprets that vast information.
Which brings me back to the original question: writing vs. speaking. A generalist philosopher will likely lose in a speaking debate against any specialized expert in a given field. The generalist simply does not have enough facts memorized to compete. But if the debate was written with no time limit, the generalist could read up on any topic to become nearly as knowledgable as the expert and defeat them in a debate using their more broad general knowledge and superior reasoning skills. Like the philosopher stuck in the weeds of philosophy, specialists can become too absorbed in their own field and lose the forest from the trees, becoming clueless about everything else.
Ultimately, an individual’s intelligence cannot be judged by either speaking or writing alone. The distinction might be personal, case by case. Generally, introverts write better while extroverts speak better. So writing might more accurately reflect an introvert’s intelligence, while speaking might better reflect an extrovert’s. For some people, staring at a blank page and needing to write causes anxiety, while for me, staring at another face and needing to speak causes anxiety—and no one is their most intelligent while anxious. I simply cannot speak as coherently as I can write—my brain is not wired that way. Other people can speak fluently and intelligently, but when forced to write they face mental blocks. Like generalism vs. specialism, neither introversion nor extroversion is inherently better—each have their strengths and weaknesses.
The act of writing one’s thoughts should not be conflated with having books and the internet to reference. If I was alone with just a pen and paper and zero reference material, I could better express my thoughts and knowledge by writing it down rather than speaking aloud. It is not the mere fact of having reference material that makes me more intelligent in writing, it is having the time and space to arrange my thoughts and edit them into coherence. But of course google helps too.
So which better reflects an individual’s intelligence: their spoken words or written words? As with most complex questions, the answer is not clearly black or white. In short, it depends.