Two questions concerning Anselm of Canterbury’s theistic argument provided in Proslogion Ch. 2 are asked and answered: is the argument valid? under what conditions could it be sound? In order to answer the questions the argument is formalized as a first-order theory called AP2. The argument turns out to be valid, although it contains a hidden premise. The argument is also claimed not to be ontological one, but rather an a posteriori argument. One of the premises is found to be (...) false, so the argument is claimed not to be sound and to fail to prove its conclusion. (shrink)