The general principles of deism may be compressed into a few theses. There is a natural religion, whose essential content is morality; this comprises not much more than the two maxims, Believe in God and Do your duty. Positive religions are to be judged by this standard. The elements in them which are added to natural religion, or conflict with it, are superfluous and harmful additions, arbitrary decrees of men, the work of cunning rulers and deceitful priests. Christianity, which in its original form was the perfect expression of the true religion of reason, has experienced great corruptions in its ecclesiastical development, from which it must now be purified. These principles are supported by the following arguments: Truth is one and there is but one true religion. If the happiness of men depends on the fulfilment of her commands, these must be comprehensible to every man and must have been communicated to him; and since a special revelation and legislation could not come to the knowledge of all, they can be no other than the laws of duty inscribed on the human heart. In order to salvation, then, we need only to know God as creator and judge, and to fulfill his commands, _i.e._. to live a moral life. The one true religion has been communicated to man in two forms, through the inner natural revelation of reason, and the outer historical revelation of the Gospel. Since both have come from God they cannot be contradictory. Accordingly natural religion and the true one among the positive religions do not differ in their content, but only in the manner of their promulgation. Reason tries historical religion by the standard furnished by natural religion, and distinguishes actual from asserted revelation by the harmony of its contents with reason: the deist believes in the Bible because of the reasonableness of its teachings; he does not hold these teachings true because they are found in the Bible. If a positive religion contains less than natural religion it is incomplete; if it contains more it is tyrannical, since it imposes unnecessary requirements. The authority of reason to exercise the office of a judge in regard to the credibility of revelation is beyond doubt; indeed, apart from it there is no means of attaining truth, and the acceptance of an external revelation as genuine, and not merely as alleged to be such, is possible only for those who have already been convinced of God's existence by the inner light of reason.