Here are two diverging ideas of what faith is.
One is the notion that faith is belief in something without any evidence to support it. This is the stance taken by most atheist materialists: that faith is merely childish acceptance of something as being true without demanding that it actually be true, or that it even be supported by any evidence of being true. Wishful thinking is sufficient, for faith, according to most who are philosophically naturalists, including modern atheists persuaded to the “New Atheist” brand of strident materialism.
That point of view is false, but it is sometimes made murky. For example, in an otherwise very fine book on reasons for Christian faith, The Case for Christ (Zondervan 1998) Lee Strobel unfortunately described faith in just this way, though it must be said that he did so even as he was discussing quite specifically and intentionally the evidence for belief, thus belying his own definition.
This view of faith has some deeper history even within Christian thinking. No lesser light than Soren Kierkegaard could be read in places to have regarded faith in this way, placing faith above reason as a way of knowing. Similarly, contemporary philosopher Alvin Plantinga revives from John Calvin a concept of faith as “properly basic;” that is, on the same level as belief based on evidence. On this view, faith as a way of knowing derives from a felt sense of God’s presence; a “sensus divinatus,” and as such is on the same plane, as a basis for knowing, as knowledge based on rational thought applied to evidence. It would be a short step from this way of thinking to the conclusion that evidence of God’s existence is unnecessary to faith, rather than considering the sensus divinatus or the rational conclusion of God’s presence as being that evidence.
Weight of Evidence
A second idea about the basis of faith is much like how we think of an endeavor of science; that is, a conclusion resulting from rational reasoning from the available evidence. The idea here is simply that the process of reasoning from evidence brings us to the conclusion that there is a God, and in the same way the Biblical revelation of God is true based on the evidence, and therefore so are Christian doctrines derived from it.
What is Evidence
This second view of faith is actually better reconcilable with the first than we might at first suppose. The reason is that both just shift our attention to what “evidence” is. Even the most unthinking, unreflective religious believer bases his faith on something. It might only be that the church says it’s true, and that the church by his lights must have some pretty good reasons for saying so. Or, it might be that a person has a better ability than most of seeing the most obvious evidence; evidence that is so obvious we might tend to look right past it, such as the astonishing fact of existence of anything. Or, it might be that one recognizes that “evidence” in a metaphysical inquiry is equivalent to “reasons,” and reasons for belief include, in addition to existence, the conclusion of rational necessity for a God, in addition to the usual philosophical proofs offered.
Biblical Concept of “Faith”
It’s easy to find the Christian view of what faith is. “Faith is the assurance of things hoped for, the conviction of things not seen” (Hebrews 11:1). What is described here is a high level of certainty, characterized by taking irrevocable steps in reliance on revealed truth in fact being true, often at great cost should that certainty be misplaced, as with Abraham’s willingness to sacrifice his son Isaac. (Hebrews 11:17). What is also described here is the subject matter of that certainty: “things not seen;” i.e., spiritual things.
So this explicit definition of faith relates to: (a) its subject matter, being spiritual reality; and (b) the degree of certainty one seeks to attain about the truth of that subject matter. Notably absent from this definition of faith is any indication that we’re to accept as true any doctrine without evidence.
This definition of faith in the book of Hebrews is sometimes quoted by atheists, rather puzzlingly, in support of the assertion that faith rests upon no evidence at all. But that’s not what this passage says. No good faith reading of Hebrews would yield the conclusion that one is to believe without having reasons to do so. Evidence for the truth of the passage is contained elsewhere in the Bible. Indeed, evidence is provided from the 750,000 or so remaining words of the Bible, in addition to God-given reason and natural revelation.
In case the purposes of this definition of faith are not perfectly obvious already, a few lines down, in Hebrews 11:3, we read that “By faith we understand that the universe was created by the word of God, so that what is seen was not made out of things that are visible.” This is a direct repudiation of materialism, but to our present point, it is not a directive to believe even without evidence for our belief. It means that the subject matter of our belief is God’s having created the universe; that matter does not create matter, God does.
If you’re a Christian, consider avoiding formulas for faith that seem to imply that it is unreasoning. And if you’re not a Christian, think about what evidence includes, and if you know the Bible, what it actually says.