Some very interesting comments concerning intellectual activities----Phoenix and Letty mentioned the ability to think in the abstract which I considered self evident but perhaps needs a review. The following is from the thinking of John Dewey, a very influential thinker on education, and is titled "from the concrete to the abstract"
http://spartan.ac.brocku.ca/~lward/dewey/Dewey_1910a/Dewey_1910_j.html
Craven has the opinion that only curiosity is required and has nothing to do with ability.
I equate ability with intellectual capacity which we all have in varying degrees and I would present an example of what I mean. It seems that all great thinkers possess two separate qualities in common.
1. An insatiable curiosity at a very young age.
2. The mental capacity to devour and absorb knowledge. This requires a very special memory capacity AND the special ability to RECALL that memory. Memory is what limits each of us----with out memory we are vegetables walking around in a human shell. Memory is strictly a bioneurological function and is determined at birth by the genetic template which in turn determines the mix of chemicals that will control the ability of the brain to formulate memory AND to establish the tracks to recall that memory. That same genetic template also determines the amount of curiosity which triggers all intellectual activity.
JL's point about the participants of this forum engaging in intellectual activity, is well taken and can only improve the ability of each of us to broaden our horizens and to stimulate what intellectual capacity we possess. IMO however, merely engaging in intellectual activity does not make any of us a true intellectual. That title should be reserved for a rare few such as Noam Chomsky (I don't agree with his political views ) or a Steven Pinker, author of the "Blank Slate". There are many others of course but the sum total of intellectuals in any society IMO would be less than one half of one percent.
There was also reference to the ability to make common sense decisions. In what little study I have done in this regard, there seems to be little correlation between intellectual capacity and ability to make sound everyday decisions. We all know of brilliant people who cannot balance a checkbook or perform other everyday functions consistently. Letty mentioned an uncle who is a brilliant businessman but no intellectual. I would guess that it is only because his curiosity has not expanded to include ideas other than those needed to make money. He may have the mental capacity to become an intellectual but right now he is having too much fun making money. However as Phoenix mentioned, one must possess the innate need to examine ideas therefore in all probability he will never be curious about other ideas----perhaps when he has made all the money he feels he needs----he may then turn to intellectual pursuits.