Whenever one says, "I just believe" or "I just believe in Jesus" and does not or cannot give reasons for why they believe that claim, they are embracing this interpretation of "faith." Really it is the kind of faith that has faith only in itself. Here's the definition.
Fideism: The view that faith takes precedence over reason. The word is often used as a term of abuse to designate a view considered by a critic to be a form of irrationalism. Tertullian and Soren Kierkegaard are often cited as fideists.(Source: C. Stephen Evans. Pocket Dictionary of Apologetics & Philosophy of Religion. Downers Grove: InterVarsity Press, 2002, s.v. "fideism".)
Application of the Definition
When you are involved in a conversation with someone who says they just believe, or that they have faith that what they believe is true, this is an example of holding to a form of fideism. Some of the tenets of fideism include existential forms of "testing" truth. There is no reason that will refute experience for the fideist. Norman Geisler in his monumental book, Christian Apologetics also includes in the tenets of fideism includes not only God's revelation, but His grace is the source of all truth (see the chapter on "Fideism" in Geisler, Norman. Christian Apologetics. Grand Rapids: Baker Books, n.d. Norman Geisler's CD Library).
At first glance this looks good to the experiential person. However it isn't if you look at what the statement is saying. First off, the Bible is God's special revelation and His grace is the means by which one is saved. We know this from the Bible. Now, we do have God's continual graces, but how do we know that these "graces" are from God?? We also know this from the Word of God and not the experience.
Remember this the next time you talk to Mormon missionaries who tell you that their experience of knowing the Book of Mormon is true is by an experiential "burning in the bosom." If you are talking to a professing Christian, and they tell you they just believe in Jesus, ask them how they know their belief is in the right direction or object of their faith. You may be talking to a fideist that needs help and encouragement because their truthclaim is based upon the experience.