The way of reason: We teach children, too, not to 'lean (too confidently) to their own understanding'; because the function of reason is to give logical demonstration (a) of mathematical truth, (b) of an initial idea, accepted by the will. In the former case, reason is, practically, an infallible guide, but in the latter, it is not always a safe one; for, whether that idea be right or wrong, reason will confirm it by irrefragable proofs.The part that puzzles me is that initial "acceptance or rejection of ideas".
Therefore, children should be taught, as they become mature enough to understand such teaching, that the chief responsibility which rests on them is the acceptance or rejection of ideas. To help them in this choice we give them principles of conduct, and a wide range of the knowledge fitted to them. These principles should save children from some of the loose thinking and heedless action which cause most of us to live at a lower level than we need.
According to the thought of St. Thomas Aquinas, human reason, to say it as such, 'breathes,' that is, it moves on a wide-open horizon in which it can experience the best of itself. Nonetheless, when man limits himself to think only of material and experimental objects, he closes himself to the questions of life, about himself and about God, impoverishing himself." --Benedict XVI, Feast of Thomas Aquinas, January 2007
From the Catholic Encyclopedia on Reason:
Ratio, in opposition to res, denotes the mode or act of thinking; by extension it comes to designate on the one hand the faculty of thinking and on the other the formal element of thought, such as plan, account, ground, etc. This wide use of the word reason to denote the cognitive faculty (especially when dealing with intrinsic evidence, as opposed to authority) is still the commonest.
....In its general sense, therefore, reason may be attributed to God, and an angel may be called rational. But in its narrower meaning reason is man's differentia, at once his necessity and his privilege; that by which he is "a little less than the angels", and that by which he excels the brutes. Reasoning, as St. Thomas says, is a defect of intellect. True, in certain acts our mind functions as intellect; there are immediate truths (ámesa) and first principles (archaí) which we intuit or grasp with our intellect; and in such verities there can be no deception or error. .... Within a certain region our cognitive faculties are absolutely infallible.
Yet the Scholastics also unanimously hold that man's specific mark is ratiocination or discursus. .... in this life our knowledge is a thing of shreds and patches, laboriously woven from the threads of sense..... our actual human experience.... is a gignómenon, a coming to be. Man is rational in the sense that he is a being who arrives at conclusions from premises. Our intellectual life is a process, a voyage of discovery; our knowledge is not a static ready-made whole; it is rather an organism instinct with life and growth. Each new conclusion becomes the basis of further inference.
Hence, too, the word reason is used to signify a premise or ground of knowledge, as distinguished from a cause or real ground. So important is this distinction that one may say herein lies the nucleus of all philosophy. The task of the philosopher is to distinguish the a priori of logic form from the a priori of time; and that this task is a difficult one is testified by the existence of the many systems of psychologism and evolutionism. Reasoning, therefore, must be asserted to be a process sui generis.I will leave it there for now. It seems to me that Charlotte Mason is using the word "reason" in the sense of the discursive process, what the CE calls "ratiocination". She holds (or it seems so to me) that the original premises or principles (she uses the term "ideas") are accepted by the will. Consequently, she says that the child's main role in dealing with ideas is to affirm or deny, which is puzzling to me. I will have to pore through Catholic philosophy a bit more to figure out if it has an equivalent notion of the will's role in accepting ideas.
This is perhaps the best answer to give to the question, so much discussed by the old logicians, as to what kind of causative influence the premises exert on the conclusion. We can only say, they validate it, they are its warrant. For inference is not a mere succession in time ; it is a nexus thought-of, not merely an association between thoughts. An irrational conclusion or a misleading association is as much a fact and a result as a correct conclusion; the existence of the latter is explained only by its logical parentage. Hence the futility of trying to account completely for the existence of a human thought--the conclusion of a train of reasoning--simply by the accompanying sense-data and psychological associations.
The Catholic Encyclopedia's definition of Will includes this (I think I've quoted it before):
This doesn't seem too far from CM's notion, but I shall have to think about it some more. I know from other reading on her notions of Will that she has a similar idea of it as being the commander of all the other parts of the human.
The term will as used in Catholic philosophy, may be briefly defined as the faculty of choice; it is classified among the appetites, and is contrasted with those which belong either to the merely sensitive or to the vegetative order: it is thus commonly designated "the rational appetite"; it stands in an authoritative relation to the complex of lower appetites, over which it exercises a preferential control; its specific act, therefore, when it if in full exercise, consists in selecting, by the light of reason, its object from among the various particular, conflicting aims of all the tendencies and faculties of our nature: its object is the good in general (bonum in communi); its prerogative is freedom in choosing among different forms of good.