Comment by jodrellblank

Of course it doesn't "do reasoning", why do you think "following the instructions you gave it in the stupidest way imaginable" is 'obviously' reasoning? I think one definition of reasoning is being able to come up with any better-than-brute-force thing that you haven't been explicitly told to use on this problem.

Prolog isn't "thinking". Not about anything, not about your problem, your code, its implementation, or any background knowledge. Prolog cannot reason that your problem is isomorphic to another problem with a known solution. It cannot come up with an expression transform that hasn't been hard-coded into the interpreter which would reduce the amount of work involved in getting to a solution. It cannot look at your code, reason about it, and make a logical leap over some of the code without executing it (in a way that hasn't been hard-coded into it by the programmer/implementer). It cannot reason that your problem would be better solved with SLG resolution (tabling) instead of SLD resolution (depth first search). The point of my example being pseudo-Python was to make it clear that plain Prolog (meaning no constraint solver, no metaprogramming), is not reasoning. It's no more reasoning than that Python loop is reasoning.

If you ask me to find the largest Prime number between 1 and 1000, I might think to skip even numbers, I might think to search down from 1000 instead of up from 1. I might not come up with a good strategy but I will reason about the problem. Prolog will not. You code what it will do, and it will slavishly do what you coded. If you code counting 1-1000 it will do that. If you code Sieve of Eratosthenes it will do that instead.