For the sake of defending the faith and teaching God's truth to others, Christian theologians and apologists (defenders of the faith) have developed a specialized vocabulary. Terms such as Trinity, hypostatic union, eschatology, aseity, and many others are employed to help people grow in their knowledge of God and His Word. With respect to the doctrine of Scripture, two words are often used in order to make assertions about the veracity of the Bible: inerrancy and infallibility.
Inerrancy means that the Scriptures do not affirm any errors. The Bible does not endorse anything untrue. When it tells history, it tells us what actually happened. It may report on what a person said when he told a lie to someone else, but it does not endorse the lie. It is merely giving an accurate report of what the liar said. Where it speaks to science, it does not contradict God's revelation in the natural world. In sum, the Bible is entirely truthful and has no errors at all in the original manuscripts that the prophets and Apostles actually wrote. We do not today possess these manuscripts, but through the process of textual criticism, we can recover the original wording of the manuscripts with a high degree of certainty.
It is important to note that inerrancy is not a property unique to Scripture. Human beings regularly make error-free statements. Students score 100 percent on exams; people accurately state their names to others; and so forth. What sets Scripture apart from all else is its infallibility. Infallibility has to do with possibilities, and it means that the Word of God is incapable of erring. We can produce inerrant documents and other things and yet still retain the possibility of erring. Before Ashley scored 100 percent on her math test, it was possible that she might miss one of the answers. When the Lord inspired the authors of Scripture, however, He worked so as to make it impossible for them to affirm error in the completed product. We can have inerrancy without infallibility, but we cannot have infallibility without inerrancy. Infallibility necessarily results in the text's being free from error; without infallibility, the production of an inerrant text is accidental. It could have otherwise had errors.
We affirm the inerrancy and the infallibility of Scripture because we know the character of God. Today's passage, for instance, tells us that the Lord never lies. If God never lies, His Word never lies either. We can therefore trust it to be free from all error.
Some people have recently used the term infallibility even though they believe the Bible does contain errors, so we need to be on guard against the possible misuse of the word. Historically, however, Christians have said Scripture is infallible because they have believed that God's Word is incapable of erring and thus contains no errors. And because the Bible gives us ample warrant to believe this, we know we can stake our very lives on the Word of God.