H. E. Booker

In Science magazine (probably around 1973)

At the conclusion of an ideal undergraduate education, a man's brain works well. He is convinced, not that he knows everything or even that he knows everything in a particular field, but that he stands a reasonable chance of understanding anything that someone else has already understood. Any subject that he can look up in a book he feels that he too can probably understand. 

On the other hand, if he cannot look it up in a book, he is uncertain what to do next. This is where graduate education comes in. Unlike the recipient of a Bachelor's Degree, the recipient of a Doctor's Degree should have reasonable confidence in his ability to face what is novel and to continue doing so throughout life.