What does Christianity mean by faith?

"Now faith is assurance of things hoped for, proof of things not seen." The chapter that follows is a list of people who acted on it, which is the sense it is being used in: trust that shows up in what somebody does.

The same chapter says "he who comes to God must believe that he exists", so propositional belief is in there. It is the floor rather than the thing being described.

James: "even so faith, if it has no works, is dead in itself", and then the sharpest line in the argument, "you believe that God is one. You do well. The demons also believe, and shudder."

On that account intellectual assent is not merely insufficient, it is the thing the opposition also has. Whatever is being commended, it is more than the state of holding a proposition true.

A father, told that all things are possible to him who believes, answers "I believe. Help my unbelief!" and his son is healed. That sentence is a contradiction on the ignorance definition, and Mark keeps it as an acceptable answer. Matthew and Luke tell the same healing without it.

Thomas refuses to accept the resurrection without putting his hand in the wound, is offered exactly the demonstration he asked for, and is not expelled. He is told "Don’t be unbelieving, but believing", and that those who believe without seeing are blessed, which is a correction and a comparison, not a condemnation.

Writing about the resurrection: "if Christ has not been raised, then our preaching is in vain and your faith also is in vain", and a few lines later, "if we have only hoped in Christ in this life, we are of all men most pitiable."

That is a claim staked on something happening, stated by the person making it, with the consequence of its being false written out. Whatever else that is, it is not immunity from evidence.

The Greek pistis and the Latin fides were ordinary words for trust, between family, friends, citizens and gods, before Christians put them at the centre of their religion. The study cited here follows both across the early Roman empire and the early churches. It argues that in the New Testament the word still means trust, and that faith as propositional belief appears in some of its writings, out of arguments among Christians and with outsiders.

How much of the modern argument is a translation artefact is genuinely disputed, and it would be too convenient to say the whole of it is.

The Catholic Catechism, the Lutheran Augsburg Confession and the Reformed Heidelberg Catechism all call faith a gift of God rather than an achievement, which changes what it means to lack it. All three join trust to assent. The Catechism calls faith first a personal adherence to God and, inseparably, assent to the whole truth he has revealed. Heidelberg calls it a sure knowledge and also a wholehearted trust. Augsburg says the word does not mean merely a knowledge of the history, such as the devil has, but confidence, which is James’s point about the demons.

How each puts it bears on a practical question: what somebody who wants to believe and cannot is supposed to do.

Nothing here settles that, and this exploration is not trying to. What it establishes is narrower and is often skipped: what the thing under discussion is claimed to be by the people who have it.

An argument against a definition the texts do not use is a waste of everyone’s time, and both sides of this one have spent decades on it.

Because some believers do use faith to mean exactly what the critics say, and say so proudly. The caricature is not invented; it is a real position, held by real people, and it is not the historic mainstream one.

And because the textual sense is harder to argue with. Trust is a relationship, and you cannot refute a relationship, which is either a fair observation about the category or a very convenient move, depending on where you stand.

Mark the claims. Where something rests on a manuscript, say so; where it rests on an argument among historians, say so; where it rests on trust, say that, and do not dress it up as either of the others.

A reader who can tell those three apart can read anything written about this subject, including the parts written to persuade them.