[JadeNB]

> "If writing down your ideas always makes them more precise and more complete, then no one who hasn't written about a topic has fully formed ideas about it."

> Apparently, even writing it down didn't help the author with this flawed deduction.

I think that it can be rescued, at some expense of awkwardness, by grouping not as one would expect ("(fully formed) ideas"), but in a slightly non-standard way:

> "If writing down your ideas always makes them more precise and more complete, then no one who hasn't written about a topic has fully (formed ideas about it)."

That is, if you haven't written about the topic, then you haven't understood it as precisely and completely as you could. While this is obviously exaggeration, I think that it's (1) logically consistent, (2) possibly what pg meant, and (3) a useful slogan, even if intentionally over-stated.