The following is an off-hand definition I made on
another thread, and was asked to re-post it separately. So do what you will with it, or not.
Determinism is the concept that all events, human actions and thought in particular, happen because they had antecedent causes that insure they will be exactly what they are and nothing else. All events absolutely have to be the way they are. Determinism and absolute randomness, are the only two agents of action, which give lie to freewill. Freewill is an illusion.
Its possibly right, but to me it depends on whether there is ultimately repetition in numbers, such as in the number line and in the digits of pi or the natural exponent. I agree things appear to be deterministic that do not operate in loops, referencing the results of their own actions. Most things have a particular beginning and then proceed deterministically from that beginning, however dynamic systems which feed back into themselves are supplemented by the number line. If the number line is truly without pattern then so are they, although that is still an 'If'.
Though experiment: Consider the super milkman who leads a charmed, uneventful life. The super milkman gets up early in order to deliver milk, picks up the milk and delivers it. The milk is delivered according to a set of predetermined causes and potentials. The same milk man delivers milk every day to the same locations with no changes in orders. His is the perfect schedule, never changing, and he and his clothes never age. His wife never ages, and his friends and his town never age. Every day he gets up, picks up the milk and delivers it again; but every morning he starts out in a slightly different way, because 'Yesterday' has affected 'Today'. Each day he begins his work with the effects of the previous day's works. His previous experiences feed back into his daily experiences, so that each day is actually different. The point here is that each day begins a typical way and proceeds deterministically, but what is the effect of the repetitions and the slight variations? Why don't the days become more and more similar until they are all exactly the same? Instead each previous day adds some sort of difference to the next day, and despite all things being the same they never are.
What is the last digit of pi? The last digit changes depending upon the accuracy you want, and as far as we know is random though possibly its not. Perhaps there is some repetition somewhere in it or some way to predict. There may be a pattern to it or not, and the question of whether things are truly chaotic probably depends upon answering questions like that one.