Groucho and Pure Jokes

My Fellow Comedists,

I was unable to get this weekend's comedist post up in time, so let's do it today.  This week marks the 50th anniversary of Groucho's last public performance.  An aging Groucho was slipping into depression, so his nurse arranged to have a one-night-only affair at Carnegie Hall called "An Evening with Groucho" where he told stories and jokes to a packed house of admiring fans.

It seems like a fine time to think about a claim made by Ted Cohen in his book Jokes: Philosophical Thoughts on Joking Matters.  Cohen draws a distinction between conditional jokes that would only be understood by a group of people who had specialized knowledge presupposed in the joke and pure jokes that could be understood by everyone.  He then claims that there are no pure jokes.  All jokes, he contends, require some specialized understanding.

Is this true?  Are there any pure jokes? 

I heard Dick Cavett on the radio recounting one of his last dinners with Groucho in which a couple came up to the table and the man asked Groucho to insult his wife to which Groucho replied that "With a wife like that you should be able to think up your own insults."   Is that not a pure joke?  What group is that restricted to?  Or what about the classic line from Animal Crackers "I got up one morning and shot an elephant in my pajamas.  what he was doing in my pajamas, I'll never know."  What is the restrictions on that one?

Are there really no pure jokes?

Live, love, and laugh,

Irreverend Steve