Faith is the deliberate will to believe, in advance of all future evidence and investigation, what one perceives to be either unsupported by evidence or even outright undermined by evidence.
In this way faith is essentially a matter of will and not just belief. Simply having a belief that is unsupported or undermined by evidence is insufficient to have a faith belief—you have to perceive that your belief is unsupported or undermined by evidence first and then defiantly choose to believe anyway. This also means that there could be some beliefs that are supported by evidence but a given believer does not know that and, despite thinking that the belief is unsupported by evidence, chooses to believe anyway. In this case, someone could hold a belief by faith even though it is actually unnecessary to do so since the belief is evidentially supported. If it is blameworthy to believe without perceiving that there is appropriate evidence for your belief (as I argue it usually is), such a person’s believing would be culpable even though the belief is warranted by evidence she does not know about (or does not properly weigh).
Some interesting things follow from this. Even though religious people the world over, throughout time, have believed many strange things which seem to modern minds utterly refuted by evidence, they have not necessarily had faith in all these strange things. Quite often they may have (and may still) perceive themselves to be responding to evidence. Their standards of evidence and their various metaphysical, epistemological, scientific, etc. assumptions may be totally erroneous. But this is due to an inadequacy of critical thinking skills and/or a lack of information, and not due to a contemptuous disregard for critical thought and subordination of reason to willfullness, like faith is.
It is rationally justifiable and appropriate for children to accept the word of their elders in a great many matters. Their default assumption has to be that unless they have reasons to doubt what they are told, that it is likely to be true since they do not themselves have the wherewithal to investigate every piece of information for themselves and they have an immense amount of information to assimilate as fast as they can. Children are rationally justified in considering their parents and teachers trustworthy guides until they give signs of untrustworthiness in specific areas. When children accept the metaphysical, ethical, and scientific guidance of their parents they are justified even if what their parents and teachers are saying is false. This is not faith as the children are not making any willful choice to reject evidence in principle but rather a justified deference to those more expert than they are.
During this period, rather than train children in the rigorous standards of critical thought which have made the modern revolution in knowledge possible, many religious people train their children to reinforce their worst, natural, human cognitive biases where it suits their religion. Many children are trained to adopt the vice of faith in this way. But this is a distinct issue from their default trust in their parents’ teachings about how the world works, which is rationally justified for them even if it means some of their beliefs are false. Sometimes we can be rationally justified in believing what it is impossible for us to know, given our situation, is false. We don’t actually have knowledge in such a situation, but we are at least blameless for our error.
So, in this context, we can understand how someone can mature into an adult with many false beliefs that, while not knowledge, were nonetheless formed through a rationally justified process of trusting the best authorities available to oneself. From our parents and teachers we learn a wealth of true things and so we are justified in our trust even though we will inevitably pick up some false ones.
Now in my experience, many religious people hold many of their religious beliefs as though they were matters of knowledge (or high likelihood of knowledge) because (a) they do not have proper training in critical thinking skills to assess them philosophically, logically, or scientifically, or through other appropriate methods and/or (b) they have not been adequately exposed to the arguments for alternative possible beliefs to the ones they trustingly learned from their parents.
So such people may not actually hold many of their religious speculations directly by faith, i.e., by a choice to believe what is unsupported by evidence and even undermined by evidence. Such people are just implicitly accepting the passed on beliefs of their religion as automatically as they accept all the other beliefs that came from their parents and teachers and tradition, etc.
Before specific, effective intellectual challenges to their beliefs arise, where their faith is really located is in a disposition to retain their religious beliefs (if not many others) even if they are undermined by future evidence. So, whereas the average religious believer, prior to serious exposure to devastating arguments, believes that God is a likely true entity and also believes that water is comprised of two hydrogen elements and one oxygen element, and believes that both these perceived truths are trustworthy, she is ready to abandon the theory of the composition of water if scientists change their teaching but she has been trained in advance to affirm the God belief even if she should encounter an intellectual challenge.
Many religious believers do implicitly think belief in God is the most rational metaphysical explanation of the universe, especially before they encounter vigorous challenge to that assumption. They do not really think they are being especially defiant of evidence. Yet their belief that faith is a virtue disposes them to defy the evidence should a strong argument be made against their belief just the way that I may have a belief in, and general disposition towards, the virtue of courage though usually I have no need for it. For many religious believers, even though they believe many strange things, they do not actively do so as matters of defiance of evidence until the case against their strange beliefs is made and then they activate their vice of faith, thinking it is a virtue.
And this is what is so insidious about faith. One begins a debate with a religious believer who, despite the strangeness of what he thinks to outsiders, finds his beliefs entirely sensible given the inculcation in him of a certain intricately interconnected and seemingly coherent view of metaphysics, epistemology, ethics, science, history etc. all together from a young age by the same people who taught him innumerable reliable, proven, practical things as well. One then brings to light for this religious believer all the inconsistencies internal to the believer’s religious system of thought and all the inconsistencies between the religious system and what is known about history and science and morality and metaphysics, etc. One creates in the religious believer cognitive dissonance and the room for doubt. One clarifies the rules of logic and the scientific and philosophical methods and attitudes and standards of evidence which have separated the modern era from areas of such slower intellectual progress. And this sensible person who believes in their religion because it made sense to them has a choice: engage in a process of correcting for all these inconsistencies by abandoning the received religious beliefs as erroneous or cling to those beliefs while admitting they are unfounded or undermined by the evidence.
Some religious believers will still insist they have the most rational account, of course. I was this kind of religious believer for most of my religious life. In retrospect, I relatively rarely had faith except for one period where I sort of did—but that’s a story for another time. But such believers who will make modifications to their beliefs about metaphysics, science, history, ethics, etc. in order to keep their religious beliefs both internally consistent and consistent with their beliefs in non-religion specific matters, to some extent are avoiding deliberately having faith. Sometimes they become rationalizers who distort their views on a host of issues just to keep their religious beliefs logically consistent with the rest of their thought and avoid cognitive dissonance.
And other times these religious believers wind up with religious beliefs that are more modified and compatible with the rest of what they know to be true. Oftentimes they are still unaware of further serious problems that would cause further need to adapt. But while ignorant of those further challenges, they still are not resorting to faith.
And of course, some of these religious believers who modify some beliefs to avoid cognitive dissonance will feel like faithfulness to their religion requires biting the bullet on some issues and adopting an explicitly faith-based, willful defiance of evidence on those select issues rather than all of them.
And some believers are so intractable that they give little or no ground whatsoever and just embrace the “nuclear” (faith) option fullthroatedly. Sometimes, such people even become outright misologists who fear and distrust reason itself.
This account, I think, explains in part why many religious believers start out thinking their beliefs completely sensible, even obviously true, and yet within the space of even a relatively short debate will wind up switching gears drastically and saying things like “but that’s why you need faith!” They often shift from thinking what they have to say should be totally comprehensible and persuasive to conceding that of course there are no good reasons for their positions but of course that’s not a reason to abandon them.
This allows religious people to convince themselves they are perfectly reasonable people who have no problem with evidence and whose religious beliefs are of course sensible (and at least likely true if not provable), even though in sudden emergencies they will become explicit enemies of evidence and reason on a dime.
And this should offer a little more insight into how faith is the poison that paralyzes religions and religious people from abandoning false beliefs and improving their practices, and, thus, why it is what is really wrong with religion and what stands in the way of truer religion (i.e. religions which are based on and reinforce truth, rather than passionately preserve and perpetuate the ossified errors of our superstitious, scientifically ignorant, and morally barbaric ancestors).
For more on faith, read any or all posts in my “Disambiguating Faith” series (listed below) which strike you as interesting or whose titles indicate they might answer your own questions, concerns, or objections having read the post above. It is unnecessary to read all the posts below to understand any given one. They are written to each stand on their own but also contribute to a long sustained argument if read all together.