The Secret Life of Pronouns: What Our Words Say About Us
by James W. Pennebaker

Really interesting book so far. Just learned that:

• the average English speaker has a 100,000 word vocabulary
• of those 100,000 words, the 20 most commonly used words (0.02%) make up 30% of our spoken and written language (they’re all “stealth/function words” (prepositions, pronouns, etc.))
• expand that to all 450 commonly used stealth/function words, and that 0.04% of our vocabulary accounts for 55% of the words we use