EVERY systematic science, the humblest and the noblest alike, seems to admit of two distinct kinds of proficiency; one of which may be properly called scientific knowledge of the subject, while the other is a kind of educational acquaintance with it. For an educated man should be able to form a fair off-hand judgement as to the goodness or badness of the method used by a professor in his exposition. To be educated is in fact to be able to do this; and even the man of universal education we deem to be such in virtue of his having this ability. It will, however, of course, be understood that we only ascribe universal education to one who in his own individual person is thus critical in all or nearly all branches of knowledge, and not to one who has a like ability merely in some special subject. For it is possible for a man to have this competence in some one branch of knowledge without having it in all.
It is plain then that, as in other sciences, so in that which inquires into nature, there must be certain canons, by reference to which a hearer shall be able to criticize the method of a professed exposition, quite independently of the question whether the statements made be true or false.
No doubt this kind of statement doesn't seem as relevant nowadays when most educated people tend to be specialists in one narrow area and know very little about anything else, but even nowadays when there is such a huge bulk of knowledge to be learned, it seems worthwhile to start from an idea that knowledge is interconnected.
Charlotte Mason seems to have something similar in mind in Education, the Science of Relations
Every child is heir to an enormous patrimony, heir to all the ages, inheritor of all the present. The question is, what are the formalities (educational, not legal) necessary to put him in possession of that which is his? You perceive the point of view is shifted, and is no longer subjective, but objective, as regards the child.
We take the child ... as we find him––a person with an enormous number of healthy affinities, embryo attachments; and we think it is our chief business to give him a chance to make the largest possible number of these attachments valid.
Finally, Cardinal Newman in Idea of a University
I have said that all branches of knowledge are connected together, because the subject-matter of knowledge is intimately united in itself, as being the acts and the work of the Creator. Hence it is that the Sciences, into which our knowledge may be said to be cast, have multiplied bearings one on another, and an internal sympathy, and admit, or rather demand, comparison and adjustment. They complete, correct, balance each other. This consideration, if well-founded, must be taken into account, not only as regards the attainment of truth, which is their common end, but as regards the influence which they exercise upon those whose education consists in the study of them. I have said already, that to give undue prominence to one is to be unjust to another; to neglect or supersede these is to divert those from their proper object. It is to unsettle the boundary lines between science and science, to disturb their action, to destroy the harmony which binds them together. Such a proceeding will have a corresponding effect when introduced into a place of education. There is no science but tells a different tale, when viewed as a portion of a whole, from what it is likely to suggest when taken by itself, without the safeguard, as I may call it, of others.