Intelligence is an extremely subtle concept. It's a kind of understanding that flourishes if it's combined with a good memory, but exists anyway even in the absence of good memory. It's the ability to draw consequences from causes, to make correct inferences, to foresee what might be the result, to work out logical problems, to be reasonable, rational, to have the ability to understand the solution from perhaps insufficient information. You know when a person is intelligent, but you can be easily fooled if you are not yourself intelligent.
Isaac AsimovOnce, when a religionist denounced me in unmeasured terms, I sent him a card saying, "I am sure you believe that I will go to hell when I die, and that once there I will suffer all the pains and tortures the sadistic ingenuity of your deity can devise and that this torture will continue forever. Isn't that enough for you? Do you have to call me bad names in addition?"
Isaac Asimov