Have you ever noticed how some of the world's smartest people have a somewhat jerky stop-and-go speech pattern, sort-of like Google's autocomplete? It's not uncommon among smart people who are careful about what they say, strive for precision, and are cognizant and empathetic to potential contextual gaps among their audience and their different levels of understanding.
Elon Musk has a similar pattern, but it's not so much a speech disorder as it is their brain is working so fast, pulling from multiple sources and considering multiple perspectives. They're auto-editing their words in real-time, revising what they're saying while considering all of the above factors and more. But sometimes they get ahead of themselves and so in an effort to be clear and precise, they backtrack a few words and rephrase, filling-in as they anticipate potential contextual gaps. This is what you're seeing.
Rather than thinking they need to see a speech therapist, view it as a mark of authentic speech by someone who strives for precision and is empathetic to their audience. When you look at it this way, you can know and appreciate that you're witnessing the genuine workings of a brilliant mind.
I once attended a panel discussion with Dijkstra and Larry Loucks of IBM, along with a couple of other professors who were completely outclassed by those two. The speaking styles were radically different: EWD was slow and very precise, it was clear that he was thinking deeply about the topics; Larry was fast, facile, and rather shallow, he was of the IBM style (he who talks loudest is in charge).
However, I have been thinking about the unique speech patterns of some accomplished individuals. My uninformed guess is that some people develop neural connections differently depending on what they do in their formative years. Feynman, in a video [1], talks about how he was able to keep accurate time while reading but not talking, whereas his friend John Tukey could keep time while talking but not reading.
If someone doesn't talk much as a kid because they spent most of their time reading or solving math problems, it might be reasonable to expect that their speech will be underdeveloped.
I have nothing but anecdotal evidence. I, for instance, cannot talk and think (perform simple arithmetic or recall something from memory or even think about the next sentence) at the same time. If I'm talking, I have to pause shortly, think and structure what I'm going to say, and then say it, and after saying it I might notice I missed something and then I rephrase it. I've recorded myself and my speech pattern is almost the same as the one in Knuth's videos. I attribute the speech pattern to not having to talk much during my formative years.
> unfortunately he's unable to present it well. His lectures are almost useless.
I don't know; I've listened to dozens of hours of his videos and found them all useful and rather clear. I've heard comments like yours from others though, and I guess there are two points:
* Of course a person at 80 will not speak the same way they did at 40. (I'm currently watching his lectures on Mathematical Writing, given when he was 49: https://www.youtube.com/watch?v=mert0kmZvVM&index=2&t=0s&lis... -- youtube has some even older videos on TeX etc but they're probably of less general interest.) Older people generally have more halting speech and the like, but this is perfectly natural. I suspect that if, for cultural or whatever reasons, you haven't spent a lot of time listening to old people and learning from them, you may just find it unfamiliar. Nevertheless, I was in the audience when Knuth gave his 2017 Christmas Lecture weeks before his 80th birthday, and a lot of the audience did seem to follow along and enjoyed it. (You can hear laughter in the expected places in the video: https://www.youtube.com/watch?v=BxQw4CdxLr8 -- so clearly not everyone feels the way you do.)
* Every person has their own speech style, their way of translating thought into sounds. Like an unfamiliar accent, it may take a few minutes or hours to get used to it. (If you care enough about the content you will.) What you get from speech idiosyncrasies (their pauses, backtracking, mistakes, etc.) that you don't get from the written word is a window into someone's way of thinking, and I find in Knuth's lectures it's much easier to follow along his thought process, than in speakers you may consider more "smooth". It's very natural and informal, even when he's discussing highly technical topics there's a lot of him that comes through, and that's very valuable IMO.
(And his speech seems well within the norm... I've seen comments like yours that sometimes attempt to diagnose medical conditions from afar; that can seem a bit excessive.)
I think he's just a humble and genuine nice person, an uncomfortable speaker perhaps.
He was a CWRU alum and came to rap with grad students around '89. He was wearing his trademark woven hoodie and jeans. We didn't get a room, he just plonked on the floor in a hallway somewhere and told stories and enjoyed nerding with us.
