First, and perhaps foremost, was the question posed in Guide of the Perplexed of what kind of knowledge it is possible for people to have of God. According to the Doctrine of Negative Theology, which Maimonides took over from Avicenna (980–1037), nothing positive can be known about God, because God has nothing in common with any other being experienced by humans, and humans have no experience of God. All that we can know is what God is not. (Negative theology is the doctrine that God cannot be known by man.)