α) St. Fulgentius of Ruspe, who is regarded as “the best theologian of his time” (468-533),(792) in his golden booklet _De Fide seu de Regula Verae Fidei ad Petrum_, says: “I rejoice that you take care to preserve the true faith without which conversion is useless, nay, impossible. Apostolic authority tells us that we cannot please God without faith. For faith is the foundation of all good [works]; it is the beginning of human salvation, and without it no one can obtain a place among the children of God, because without it no one can obtain the grace of justification in this world or possess eternal life in the next.”(793) St. Fulgentius was a faithful disciple of St. Augustine, and the whole trend of his treatise shows that by _vera fides_ he understands not the Lutheran _fiducia propriae iustificationis_, but Catholic belief in revealed truth.(794) β) This teaching is corroborated by the ancient practice of instructing the catechumens in the truths of revelation and requiring them to make a public profession of faith before Baptism. It was because they believed and professed the true faith that the early Christians, who knew nothing of the Lutheran _fides fiducialis_, were called “faithful” (_fideles_, πιστοί), to distinguish them from false believers or heretics (_haeretici_, αἱρητικοὶ, from αἱρεῖσθαι to choose), who denied some portion or other of the orthodox creed. c) In analyzing the notions of _fides_ and _necessitas_ theologians distinguish between _fides explicita_ and _fides implicita_, and between _necessitas medii_ and _necessitas praecepti_. _Fides explicita_ is an express and fully developed belief in the truths of revelation; _fides implicita_, a virtual belief in whatever may be contained in a dogma explicitly professed. I make an act of implicit faith when I say, for instance: “I believe whatever the Church teaches,” or: “I heartily accept whatever God has revealed.” The _necessitas medii_ is based on the objective relation of means to an end, and consequently binds all men, even the ignorant and those who are in error without their own fault. Such, for example, is the necessity of the eye for seeing, of wings for flying, of grace for performing salutary acts, of the _lumen gloriae_ for the beatific vision. The _necessitas praecepti_, on the other hand, is founded entirely on the will of God, who positively commands or forbids under pain of grievous sin, but is willing to condone non-compliance with his precepts when it is owing to guiltless ignorance. This applies to all positive divine precepts, _e.g._ the law of fasting and abstinence. It is to be noted that the _necessitas medii_ always involves the _necessitas praecepti_, because God must needs will and impose upon us by positive precept whatever is objectively necessary as a means of salvation.