I've thought about your questions on and off throughout the day, and my lame response is:

It depends. It really does depend upon a lot of factors to consider, and those factors have a lot to do with the personality make-up of the individuals.

Here are some of the things that come into bearing on how much a person can understand in normal interactions:

l. Context
2. Body Language
3. Whether you're in a social or professional situation (or others)
4. Whether you're reading or speaking and listening
5. Whether you have an interest in increasing your language skills with regard to comprehension
6. Whether you have an interest in increasing your ability to communicate better orally
7. Whether you have an interest in improving your writing skills
8. Whether you have perhaps a gift for spinning a good tale, so you listen pretty carefully to how other gifted tale spinners spin theirs

These are just a few considerations I brainstormed. I can think of people who do not speak well, yet their comprehension is great because they are pensive people who have a sensitivity for language.

I can think of people who may not have great language skills, but possess gifts in the visual arts that I can only appreciate as an outsider. The same goes for music--there are some musicians who may not be brilliant conversationalists, but can they ever communicate brilliantly through their music.

We had a discussion about numbers of words in an average person's vocabulary last week, I think it was, and there was some ridiculous citation from Newsweek, if the citation was correct, about an inordinantly high number of vocabulary words in the average high school graduate's vocabularly. I'd toss that one out, W'On, and say that probably the range is between 8 and 10 thousand for high school grads, and somewhere between 8 and 12 thousand for college grads. If you wanted to be privy to somewhat cognitively-laced conversations, you'd want at least the vocabulary of the high school grad; if you just wanted to communicate fairly intelligently without many specialized terms, then probably a 6th grade education would do the trick, especially if you threw in natural gifts for making language fun, such as use of metaphors and puns.

Your questions are wide-ranging here, so I'm just taking a first jab at them to open up the discussion among others here. What we have to realize is we have the ability to read publications, such as newspapers and magazines, without understanding every single word we read. (I use "we" loosely. It's hard for us word hounds to realize that a lot of people never bother with looking up definitions and get their understanding from context and next from a word becoming popularized through repeated appearance in the news, on televisions shows, on the radio, in magazines, and so on.)

And I'll throw out one more idea: Performances in which the face tells so much--in which an actor expresses so much through the face--Jodie Foster in "Nell"--Holly Hunter in "The Piano". There's communication without words that can touch you more than a barage of words. There's communication that is received well--and that that isn't.

So, I think your topic is an enormous one.

How many words do we need? Well, it depends. It depends upon what we need 'em for, how we're gonna use 'em, and the people we're gonna use 'em with...

My take,
WW