Causality is the law of identity applied to action. Things act in accordance with their identity. So, when dealing with certain physical entities, for example, billiard balls, mechanistic causality does lead to a determined outcome based on the nature of the balls (identity), their starting conditions (context) and whatever new factor is introduced (billiard cue). We can geometrically determine the outcome.
When asking this question, though, most people are asking about human beings. The notion of determined action as applied to humans smuggles in the notion that in some essential sense, man is like a billiard ball. But man's identity includes such characteristics as the capacity to choose (volition) and his mind (reason) in addition to his physical qualities. So causality, in man's case, leads to him having the capacity to act rather than merely being acted upon as mechanistic causality would suggest.
The nature of man includes volition. Acting on that nature is still causal. It is just not mechanistic. And so it is not deterministic.
answered Dec 26 '10 at 12:38
A comment by the author of the original question states: "we are capable of making decisions on our own (volition)...."
Depending on exactly what kind of evidence is being offered in support of the view of man as determined and lacking volition, greater precision in the meaning of "volition" will be helpful. Objectivism recognizes that there are a great many automatic elements in human consciousness, such as sense-perception, emotions, and automatization of knowledge and values (sense of life). The directing of one's sensory-perceptual attention is affected by volition to some degree, but the sensory-perceptual process itself is automatic. Similarly, the values that underlie man's emotional responses are open to volition, but the link between one's values and one's emotions in response to stimuli is automatic. Objectivism identifies only one aspect of human consciousness as directly volitional: the choice to focus one's conceptual faculty or not. All other conscious choices that man makes are, according to Objectivism, "higher-level" choices that depend on the choice to focus or not. Higher-level choices develop very differently if one chooses to focus, as compared to what happens if one doesn't.
On the other hand, if the alleged evidence of determinism in man is primarily extrospective, such as some kind of brain probes and mind-brain correlations, or appeals to the atomic theory of matter and laws of physics (etc.), then the challenge for those who try to appeal to that kind of evidence is to explain and integrate their theory with man's introspective observations about the choice to focus or not. The onus of proof is on them. (Even here, precision in defining what volition is, conceptually, is essential, to bring into sharp focus exactly what is to be explained.)
Objectivism also points out that there is a fundamental contradiction in determinism as applied to man, if determinism is taken to mean that man has no power to resist persisting in an error. Human cognition on the conceptual level is fallible. If man's consciousness is determined, such that he cannot correct his errors, then he cannot know whether anything he believes is true or not. He may be mistaken, but prevented by determinism from correcting his error or even realizing that he is making an error. That is why determinism leads to skepticism.
A related question is: what is the "survival value" of the choice to focus or not, i.e., the capacity to unfocus one's conceptual faculty? If focusing is so important for reasoning and human survival, why didn't man evolve with his conceptual faculty always automatically in full focus all the time? My own tentative hypothesis is, again, precisely the value of being able to dis-engage one's conceptual faculty in the face of an apparent error, then step back and take a higher level view of what one is doing, why it appears to be leading into error, and what to do differently to resolve the apparent error (if one has confirmed that there is, indeed, a real error in one's thinking, or valid reason for doubt).
It helps a lot to think about cause and effect as being invariant. Where a given cause exists, the corresponding effect comes to pass, without possibility of exception. Anything you consider might be determinate must exhibit this relation.
So, for example, if you consider that belief in God is determinate, you must be able to give an account of some set of circumstances and relations shared by all and only those who believe in God. You have to meet the inductive minimum requirements. Perhaps you name factors which turn out to be irrelevant. That doesn't matter, as long as you can identify a correlative set of factors. And if you do not have that basis? Then, your supposition is arbitrary. It is arbitrary and doesn't deserve notice.
It is important to know when one is being asked to join a discussion of the arbitrary, but it is also important to know when one is entertaining a merely arbitrary assertion. If belief in God were determinate, there would be a set of factors in evidence (some more easily known than others, perhaps) that bear the appropriate relation to the positive and negative cases of belief in God. If there is no such body of evidence, the only reasonable conclusion is that the claim is arbitrary.
It is a license often encountered, that some immense principle is put forth, then the flip side of the arbitrary (ignorantiam) is called into effect: prove that it isn't so.