When a person says he has faith in something like the virgin birth of Jesus or the existence of God; he means he accepts ideas without any evidence. When they make the claim that people have faith in some scientific theory or objective philosophical idea they merely mean that people are confident about the truth of that idea. When people use the word faith they are often referring to two separate things, authentic faith and confidence.
Faith may be one form of confidence. But not all confidence is faith. When the word faith is used to refer to belief in probability or objective certainty rather than certainty without justification it is used that way for a reason. Belief in some level of probability (even up to complete certainty), confidence, can be justified. It may be based on clear reasoning from all the available evidence. Belief without or against evidence cannot be justified. It is self deception (for anyone above the mental level of a child) and the most prevalent form of irrationality. While science and philosophy give us the understanding of reality we need to live and live well; faith kicks reality off to the side as irrelevant and motivates men to act against its requirements (the requirements of their lives) which it leaves unrecognized and unmet. For this reason authentic faith is evil, is anti-human life. The word is used in this way to drag the good down to the level of evil or to elevate the evil to the level of the good through confusion and word games. This is an instance of what is called a package deal.
“’Package-dealing’ is the fallacy of failing to discriminate crucial differences. It consists of treating together, as parts of a single conceptual whole or ‘package,’ elements which differ essentially in nature, truth-status, importance or value.” -Ayn Rand
Faith and confidence are two very different things. To use the first to refer to the later is an attempt to force the possible legitimacy of the later on to the first or worse, to slop the illegitimacy of the faith onto confidence. They do it to rationalize their own dishonest approach to ideas in their own minds and the minds of their victims or to demoralize their epistemological enemies. To say to science and rational thought more broadly “You do it too! I might have faith in my nonsensical ideas but you have ‘faith’ in your ideas too!” But to attempt to justify ones actions by labeling what someone else does with the same word you use to refer to your own corrupt actions does not change the facts. To disentangle this form of deception one need only ask “What is meant by the word in each case? Doesn’t the kind of ‘faith’ I have differ in some important way from the faith of a mystic?”
There is no authentic faith involved in science or philosophy qua philosophy. Although religion and philosophy can be mixed together in the same mind or system; philosophy is essentially an attempt to find natural explanations for thing. Looking at reality and drawing rational conclusions from what you see is not the equivalent of accepting ideas about a super-nature. Religion is essentially a belief in something supernatural without or against any evidence. Belief without or against any evidence is what faith is. This is what differentiates the concept of faith from all other concepts. Of all the possible methods of accepting an idea this is the one that lacks concern for evidence. We already have a perfectly good word to refer to confidence which doesn’t create any confusion: the word confidence. Science and proper philosophy are diametrically opposed to religion and faith. In terms of everything essential they are antithetical.
The opposite of faith is reason from observation. Reason, not faith, is employed in science and proper philosophy. “Reason is the faculty that identifies and integrates the material provided by man’s senses.” It is by the method of logic applied to observation that we actually know anything. It is by this method that living is possible to us. To use the word faith in such away as to lump these two extremely different things together is an epistemological crime. The evil is not the good nor is the good the evil. Your life and flourishing are dependent on one and subverted and frustrated by the other. Confidence is not faith.