The systematic theosophy of Plotinus and his successors does not belong to the present article, except so far as it is the presupposition of their mysticism; but, inasmuch as the mysticism of the medieval Church is directly derived from Neoplatonism through the speculations of the pseudo-Dionysius, Neoplatonic mysticism fills an important section in any historical review of the subject.
The general presupposition involved is that a man cannot be saved except within the Catholic Church.
It presents itself historically as an intellectual revolt against the difficulties involved in the presupposition of theistic and polytheistic systems, and in philosophy as an attempt to solve the dualism of the one and the many, unity and difference, thought and extension.
The idea of a perfect harmony of thinking and being is a presupposition that underlies all knowing but cannot itself be realized in knowledge.
That the deists appreciated fully the scope of difficulties in Christian theology and the sacred books is not their most noteworthy feature; but that they made a stand, sometimes cautiously, often with outspoken fearlessness, against the presupposition that the Bible is the religion of Protestants.