Faith means believing things without evidence, which is irrational

Why many people think this

Some believers do treat faith this way. "Just have faith" can sound like "stop asking questions." And there's a popular image of faith as a leap in the dark, choosing to believe something precisely because you can't prove it. If that's what faith is, critics are right to be wary.

That's not the biblical meaning

In the Bible, faith is not believing without evidence; it's trusting based on good reasons. The Greek word pistis is about trust, loyalty and confidence. The Gospels present eyewitness testimony and signs so that people may believe (John 20:31). Paul appeals to witnesses of the resurrection who could be questioned (1 Corinthians 15). Luke begins his Gospel by saying he carefully investigated everything. That's not blind faith.

John Lennox, an Oxford mathematician, makes the point in Can Science Explain Everything? that faith is like trusting your spouse: it's based on evidence of their character, even though it goes beyond what can be proven mathematically.

Everyone lives by faith

Science itself rests on assumptions that can't be proven scientifically: that the universe is orderly, that our minds can understand it, that the future will resemble the past. Scientists have good reasons to trust these, but they are trust nonetheless. And in everyday life, we trust doctors, historians, friends and pilots, based on evidence, without absolute proof. Faith in that sense isn't the opposite of reason; it's part of how reason works.

Faith and doubt

C.S. Lewis argued in Mere Christianity that faith is partly the art of holding on to what your reason has accepted, despite changing moods. You might be convinced that an anaesthetic is safe, but feel panic as the mask comes down. Faith, in that sense, isn't believing without reasons; it's continuing to trust when feelings waver.

What are the reasons?

For Christianity, the reasons include arguments for God's existence, the historical evidence for Jesus's resurrection, and how well the Christian worldview explains human experience. Those are explored on Is there a God? and Is Christianity true?.

A fair concession

Some Christians do use "faith" to avoid hard questions, and that does real harm. Believers should welcome tough questions.

How to explain this to a friend

When a friend says faith is believing without evidence, ask them how they trust their closest friend or a good doctor. Usually it's based on experience and evidence, but goes beyond absolute proof. That's much closer to what the Bible means by faith. From there, you can offer to look at some of the reasons Christians give, which shows you're not asking them to switch off their mind.

The bottom line

Faith, as the Bible means it, is trust based on good reasons, the way you trust a friend. It's not the opposite of evidence. For more, see Can science and faith coexist?