Analogia Fidei is a principle of biblical interpretation which supposes that since the Scripture has one Author, it cannot contradict itself and therefore, the primary interpreter of Scripture is the Scripture itself. The Westminster Confession states:
The infallible rule of interpretation of Scripture is the Scripture itself: and therefore, when there is a question about the true and full sense of any Scripture (which is not manifold, but one), it must be searched and known by other places that speak more clearly.
Charles Hodge concurs. In his book Systematic Theology, he wrote:
“If the Scriptures be what they claim to be, the word of God, they are the work of one mind, and that mind divine. From this it follows that Scripture cannot contradict Scripture. God cannot teach in one place anything which is inconsistent with what He teaches in another. Hence Scripture must explain Scripture. If a passage admits of different interpretations, that only can be the true one which agrees with what the Bible teaches elsewhere on the same subject.”
The principle is taken from Romans 12:6 (kata tes analogian tes pisteos- “according to the analogy of the faith”).