Mortimer Adler on Teachability

Lately I've been reading How to Read a Book by Mortimer Adler.  And yes, the irony of reading a book about how to read books isn't lost on me.  
As I was reading this morning, I came across a great quote about teachability.  I especially value the way he points out that critical thinking is not a negative trait to have.  

"We are discussing here the virtue of teachability - a virtue that is almost always misunderstood.  Teachability is often confused with subservience.  A person is wrongly thought to be teachable if he is passive and pliable.  On the contrary, teachability is an extremely active virtue.  No one is really teachable who does not freely exercise his power of independent judgment.  He can be trained, perhaps, but not taught.  The most teachable reader is, therefore, the most critical."  (page 140 - italics are Adler's)