Doctrines stand to principles, as the definitions to the axioms and postulates of mathematics. Thus the 15th and 17th propositions of Euclid's book I. are developments, not of the three first axioms, which are required in the proof, but of the definition of a right angle. Perhaps the perplexity, which arises in the mind of a beginner, on learning the early propositions of the second book, arises from these being more prominently exemplifications of axioms than developments of definitions. He looks for developments from the definition of the rectangle, and finds but various particular cases of the general truth, that "the whole is equal to its parts."
2.
It might be expected that the Catholic principles would be later in development than the Catholic doctrines, inasmuch as they lie deeper in the mind, and are assumptions rather than objective professions. This has been the case. The Protestant controversy has mainly turned, or is turning, on one or other of the principles of Catholicity; and to this day the rule of Scripture Interpretation, the doctrine of Inspiration, the relation of Faith to Reason, moral responsibility, private judgment, inherent grace, the seat of infallibility, remain, I suppose, more or less undeveloped, or, at least, undefined, by the Church.
Doctrines stand to principles, if it may be said without fancifulness, as fecundity viewed relatively to generation, though this analogy must not be strained. Doctrines are developed by the operation of principles, and develope variously according to those principles. Thus a belief in the transitiveness of worldly goods leads the Epicurean to enjoyment, and the ascetic to mortification; and, from their common doctrine of the sinfulness of matter, the Alexandrian Gnostics became sensualists, and the Syrian devotees. The same philosophical elements, received into a certain sensibility or insensibility to sin and its consequences, leads one mind to the Church of Rome; another to what, for want of a better word, may be called Germanism.
Again, religious investigation sometimes is conducted on the principle that it is a duty "to follow and speak the truth," which really means that it is no duty to fear error, or to consider what is safest, or to shrink from scattering doubts, or to regard the responsibility of misleading; and thus it terminates in heresy or infidelity, without any blame to religious investigation in itself.
Again, to take a different subject, what constitutes a chief interest of dramatic compositions and tales, is to use external circumstances, which may be considered their law of development, as a means of bringing out into different shapes, and showing under new aspects, the personal peculiarities of character, according as either those circumstances or those peculiarities vary in the case of the personages introduced.
3.
Principles are popularly said to develope when they are but exemplified; thus the various sects of Protestantism, unconnected as they are with each other, are called developments of the principle of Private Judgment, of which really they are but applications and results.
A development, to be faithful, must retain both the doctrine and the principle with which it started. Doctrine without its correspondent principle remains barren, if not lifeless, of which the Greek Church seems an instance; or it forms those hollow professions which are familiarly called "shams," as a zeal for an established Church and its creed on merely conservative or temporal motives. Such, too, was the Roman Constitution between the reigns of Augustus and Dioclesian.
On the other hand, principle without its corresponding doctrine may be considered as the state of religious minds in the heathen world, viewed relatively to Revelation; that is, of the "children of God who are scattered abroad."