Andy Wood,
Why the goal criterion? Every creature might be said to be engaging in goal-directed activity without actually having said goal. Also, what if the very goal of intercepting the ball is not intelligent?
Admittedly, the "mental" aspect of "mental ability" might be difficult to apply to computers. Perhaps it would be an improvement to say intelligence is cognitive ability or facility. Mental abilities can take many forms and can be used in pursuit of many goals, but I think it is the abilities themselves which constitute intelligence. One who has better "mental abilities" will be better at pursuing their goals - whatever they might be - and indeed, better at determining which goals to pursue.
Anyone have any problems with defining intelligence as simply "mental ability"? People are intelligent in different ways, in accordance with their mental abilities, and IQ tests measure different aspects of intelligence by measuring different mental abilities.
Andy,
I get what you're saying, and I actually think most people would agree that a fly has a degree of intelligence, just not much. There is merit in your point about goals.
I thought that's what I was doing. If you look at the "machinery" of intelligence, you find various cognitive faculties, AKA "mental abilities." The ability to do basic math is a cognitive faculty which is necessary for the pursuit of certain goals, and a factor in intelligence. The better one is at math, the better one is at pursuing certain goals, and the more intelligent one is in certain ways. Same for other faculties.
How would you define self-direction? I'm not sure a fly has self-direction, though it can be said to have a modicum of intelligence. Flies act solely on instinct, no? If they're just responding automatically to their environment based on their evolved instincts, then in what sense do they have self-direction?