In the context of your Q, comparing "faith" vs. "knowledge" as defined in the Q is like comparing apple and orange:
- The "intellectual content" of a person's faith (in its intellectual assent aspect) vs
- The whole of Christian system of truth presented as JTB
A typical believer would fill his/her intellectual content for rational assent (#1) from an assortment of Bible, Church teaching, and apologetic books until his reason is satisfied enough to make a decision to trust Jesus as his/her Lord and Savior. Some place heavier emphasis on apologetic books, some on Bible alone, but whatever way they use to "fill" and "integrate" those knowledge into their mind, the act is equally rational because the personally-customized content comes from a rational source (which can be demonstrated as JTB in #2). The bar set for this type of "justification" varies depending on how much the individual needs to satisfy their reason so they can then trust Jesus.
But the way you define "knowledge" in your Q has to do with #2, and it's the collective effort of all Christian intellectuals (like Alvin Plantinga) to defend the Christian system as JTB. He is doing the service for the whole church so that all Christians can appeal to his work to externally "justify" the Christian system they have appropriated and integrated into their minds. The bar set for this type of "justification" of course needs to be as high as possible as can be done to meet 21st century challenges.
We should distinguish 3 types of knowledge here:
- A. Knowledge of the existence of God (which can be acquired experientially from nature by each person)
- B. Knowledge of what the Bible and/or the church teaches
- C. Knowledge of how to defend B as JTB
An individual Christian:
- knows A naturally (and is judged by God on this basis)
- needs to fill the "intellectual content" of his/her faith with B and "outsource" B's justification as JTB to a church or to an expert like Alvin Plantinga
- does not need C unless he/she is inclined to do so
The Christian then incorporates the above personalized knowledge into the trust aspect of his/her faith in concert with the grace given by the Holy Spirit, thereby increasing his/her faith as virtue. Knowledge does not increase, but trust. Optionally, the Christian can deepen their philosophical acumen to defend his/her faith (with C) but this should not be confused with the increase in faith.
Two aspects of faith
GotQuestions article What is the definition of faith? helps us separate two aspects of "faith":
intellectual assent: the aspect dealt with by Alvin Plantinga in his 2000 magnum opus Warranted Christian Belief and the 2015 popular version Knowledge and Christian Belief in which apologist Cameron Bertuzzi claims that Plantinga has overcome the Gettier problem (see Part 2 of his short blog article series Can We Know that Christianity is True). Here, "knowledge" is the object of our intellect's assent, which is obtained from various trustworthy sources (Bible, church, textbooks, etc.).
trust: the aspect implied by most NT verses that use the word "faith" (Gr pistis).
It is extremely important to separate the two aspects although in Christianity, faith is rational, meaning that
- the intellectual assent aspect should be present in a person's trust of God and Jesus (otherwise, it can degenerate into superstition / magic)
- rational does not mean the believer is responsible to personally defend the object of their assent as JTB, but merely to delegate the defense to others whom he/she trusts (like the Magisterium or Alvin Plantinga). The believer's responsibility is to show that it is rational to trust them.
PLEASE NOTE that faith is rational does not imply intellectual assent is sufficient, because in Christian theology, the aspect of trust is primary. God does not evaluate a person's faith by the correctness of the object of our intellect's assent but by the quality of our trust (which should result in good works as proof of its quality).
The corollary is that it is very important to inspect the context of the verse that use the word "faith" so we understand which aspect the author is using. For example, in James 2:19, the author is obviously talking about intellectual assent ONLY since demons don't trust God as a being who love them and who make a claim on them (as "lover's demand") to love Him back. In contrast, Acts 16:31 includes both aspects. An evangelist presents the story of Jesus coming to the world to die for us as an object for intellectual assent through good rhetoric backed by authentic revelation recorded in Scripture, but "believe in the Lord Jesus" in that verse obviously requires the trust aspect that only the hearer can produce (with the help of the grace given by the Holy Spirit).
What is the kind / nature of the knowledge that is assented? It is propositions from the Bible or church doctrine, which is "justified" through a JTB defense, or other type of apologetics in the area of epistemology. Because that kind of knowledge is about God (a living being) we should not expect the same kind of epistemological justification that we expect from mathematical knowledge, which deals with dead logical propositions.
Answering your questions
Now we are ready to answer your questions.
Do (some) Christians claim to "know" that God exists? If so, do (these) Christians use the JTB (justified true belief) definition of "knowledge", and if so, what counts as "justification"?
Answer: Knowing God exists is a lot simpler to show (using Aquinas's five ways, for example) than defending key parts of the Christian system (Trinity, Incarnation, theodicy, etc.) using JTB. Knowing God exists can also be had experientially (without philosophical articulation) by virtue of our human nature intuiting God from external nature. As described above, a typical believer would not use JTB definition of this "knowledge" but simply appeal to the veracity of the Bible and/or the church, which in turn is responsible to justify that "knowledge" using various approaches including JTB.
So we have 3 types of "knowledge" with their own type of "justification":
- knowledge from experience (such as monotheistic God)
- knowledge from authority (trusting the veracity of propositions from the Bible and the church)
- knowledge from philosophy, theology, hermeneutics, etc. (including JTB defense).
How you define "justification" in the context of justified true belief in the proposition that Christianity is true.
Answer: "Justification" in JTB refers to a professional Christian philosopher's defense to account for what happens when a regular Christian (even those without knowing any philosophy) assents to a number of propositions about God and Jesus. In the short answer, this "justification" refers to what happens when a believer fills his/her mind with knowledge type B and believe the B knowledge to be true. The philosopher is defending the lay Christian of acting rationally. This philosopher produces knowledge type C: knowledge gathered when we read Plantinga's book, for example, in order to become a better apologist.
Is this the sort of justification that any rational person can follow in order to arrive at the same conclusion?
Answer: A big fat NO. This personal justification has to do with a personal priority so a would-be-believer can satisfy his reason before trusting Jesus, and depends on temperament, upbringing, cultural environment, etc. Typical believers would read the Bible and/or church-sanctioned secondary books (such as C.S. Lewis's Mere Christianity or Josh McDowell's Evidence that Demands a Verdict, Alvin Plantinga's Knowledge and Christian Belief, or a seminary Systematic Theology textbook, etc.) for this "personal justification" task. Kids who grow up in church would just trust their Sunday school teachers and their pastors in their catechism classes. None of them need to take Philosophy 101. Regardless of how they come to the same conclusion (that Jesus is Lord and Savior), a "personal justification" should be sufficient so that when they are asked: "Why are you a Christian", they can give a rational answer. In other words, JTB is a ready-made defense for how a "regular Joe & Jane" uses externally-obtained knowledge and personally justifies their selection to come to trust Jesus as Lord and Savior.
Why do so many atheists lack intellectual assent with respect to the proposition that Christianity is true?
Answer: I propose 3 possible causes:
- They treat Christianity (as a system of truths) as needing to be justified like a natural science like Physics before they can assent to it, thus raising the bar unnecessarily.
- They mistakenly associate "having rational faith" with "being able to personally do JTB" which is normally done only by Christian philosophers. Again, they raise the bar unnecessarily. Very, very few Christians can articulate JTB defense like Alvin Plantinga. Their responsibility is to integrate authoritative propositions comfortably in their mind so they don't have too much cognitive dissonance or too much objections that can hinder their Christian practice as a rational person.
- They neglect to take into account the subjective dimension of their reason to compensate for the partial certainty of JTB defense of the Christian system, because partial is the best there is. See my answer to your other question.
Is faith defined as a special kind of belief?
Answer: No. Faith is a virtue to trust Jesus, which can grow from a small mustard seed to the kind of faith that martyrs would have (who trust Jesus enough so we can die for Him). Belief in the context of your Q is an operation of the mind analyzed philosophically, which is the intellectual aspect of faith, BUT not its primary aspect. "Blind faith" is faith without its intellectual component, which is discouraged in Christianity.
What about the relationship between faith and justification?
Answer: "justification" in the context of your Q has to do ONLY with the intellectual aspect of faith, part of a philosophical analysis of the basis for the intellectual assent. For Christians who are intellectually inclined (like you and I) we read philosophical defense of the rationality of faith. It is not strictly needed, as Christians who have deep faith don't necessarily able to articulate with philosophical precision (not to mention "justifying" it like Alvin Plantinga) the intellectual content of their faith. The Bible is clear that it is better to be a person who has faith that produces fruit than to be a person who can write a book about faith containing how to justify the intellectual component of the Christian faith.
Is faith a belief that is justified? Is faith a belief that is unjustified?
Answer: Again, to avoid getting confused, remember that faith is a virtue. What is virtue? Virtue is a disposition which helps one to do good. How does one do good? The mind has to plan it first, and as a rational faculty of the intellect, the mind relies on doctrines it learns from the church. The mind learns intellectually that this world is temporary, so health and wealth should not be the primary consideration, but love. For example, if a Catholic has a strong enough faith, he/she can relinquish wealth and become a Jesuit / Dominican, for the love of Christ. It's the church that justifies these doctrines / "belief" (the object of the intellectual assent) employing apologists like Alvin Plantinga, Cameron Bertuzzi, etc, but it's the Christian who ACTS on it with trust. The topic of James 2 is to rebuke Christians who only have intellectual assent but no trust, like the demons.
If justified, how is it different from knowledge?
Answer: In the context of your Q, as explained above, "knowledge" is the much broader category, while "justified true belief" is a special kind of knowledge pertinent to God, which a Christian uses as an intellectual aspect of his/her faith to trust God. Different areas of life need different kind of "knowledge". Unlike engineers, Christians do not need mathematical knowledge (with its associated mathematical proofs for justification) for practicing their faith because
- it is about relating to God (a living being), just like we don't need mathematical proof to trust our spouse but rationally sufficient (not exhaustive) assurance for the mind
- it's not the job of the believer, but the job of the church to present the best way to justify the beliefs that she ask a Christian to assent
When I just graduated high school, one of the most pressing issue for me was to understand what it means to believe. The Reformed church in which I grew up adamantly taught that you are saved by faith, not by works. At the time I didn't realize that the correct formula was "justified by faith" not "saved by faith", so I was under the wrong impression that "works" don't matter at all. After all, isn't that what sola fide mean? Am I not a Protestant? I thought to myself: "this is too easy, are you sure this is right?" Then when I start to doubt this doctrine I asked myself "am I losing my faith?"
I asked a Navigator staff member ministering in my university, and he asked back in a typical Reformed way, whether I believe that Jesus is my savior. I answered, "Yes", because I never doubted Jesus is God and that He died for my sin. The Navigator then said that I should have nothing to worry about: the fact that I acknowledged Jesus is my savior was sufficient to show that I have faith.
I wished he had clarified what faith means, that:
- faith in Jesus is different than trusting a particular church to teach doctrines about Jesus
- faith in Jesus is different than epistemic certainty of certain facts (i.e. resurrection, Jesus is God incarnate, etc.)
- faith in Jesus is different than understanding theology to the level of a seminary student
- faith in Jesus is different than our spiritual up and down
Although all the above 4 aspects (choosing a church whose teaching you can accept, subscribing to key doctrines, understand what faith means, feeling far/near to God) are related to faith in Jesus, the essence of faith is not the knowledge, but how we act on the knowledge: how far we are willing to take risk / sacrifice our comfort to do what is right and loving for the sake of Christ. That's why James 2:17 said (NLT):
"So you see, faith by itself isn’t enough. Unless it produces good deeds, it is dead and useless."
Now I see that the meaning of "faith" in that verse is mere intellectual assent based on knowledge understood as "justified true belief", and it's not enough. I still believe in sola fide, and I am still a Protestant, but now I see more clearly what "believe in the Lord Jesus" mean:
not satisfied in intellectual assent alone (i.e. knowing that I have been justified and adopted son of God) but continue grieving (repenting) of my failures to love, imploring Lord Jesus for grace and trusting that He will not give up in transforming me, so that I can grow in love proven by my action.
1-2=-1. Faith is when I'm taught that
1-2=-1and I either trust/accept the authority of the person who says so, or I'm made to fear the possibility of being thrown into hell for eternity if I didn't accept it or threatened with social isolation or other forms of punishment. For all of you who only had faith about negative numbers, it'd be pleasant surprise to learn that it represents the concept of lending: en.wikipedia.org/wiki/Negative_number#History