The Greek particle ei (εἰ) is the standard word for 'if' or 'whether' in Classical and Koine Greek. It introduces conditional clauses and appears hundreds of times across the New Testament. The type of conditional it introduces (simple fact, uncertain possibility, unfulfilled condition) is determined by the mood of the verb that follows.
The particle ei is one of the most theologically charged words in the New Testament, despite its simplicity. Jesus' temptation in the wilderness turns on it: 'If you are the Son of God...' (Matthew 4:3, 6) — Satan's conditional is not genuine doubt but a taunt designed to provoke Jesus into proving Himself outside the Father's will. The most powerful 'if' in Scripture may be Romans 8:31: 'If God is for us, who can be against us?' — where the conditional is used rhetorically to make an absolute affirmation. First Corinthians 15:14 uses ei in a devastating logical argument: 'If Christ has not been raised, our preaching is useless and so is your faith.' The conditional tests every claim to see if it stands.