Knowledge has been defined as firm belief in what is true on sufficient ground. The explanation of this definition which Locke gives is well known to every student of philosophy. “If any one is in doubt respecting one of Euclid’s demonstrations, he cannot be said to know the proposition proved by it; if again he is fully convinced of anything that is not true, he is mistaken in supposing himself to know it; lastly, if two persons are each fully confident, one that the moon is inhabited, and the other that it is not (though one of these opinions must be true), neither of them could properly be said to know the truth, since he cannot have sufficient proof of it.”[46]
Belief.
The foregoing definition consists of three parts,—1, firm belief; 2, in what is true; 3, on sufficient ground. In common parlance, belief is distinguished from knowledge, the latter implying a higher degree of assurance than the former. In some treatises on psychology belief denotes all forms of assent, including the highest possible certainty and conviction. The expression firm belief excludes the element of doubt from knowledge.
Truth.
Truth, according to the etymology of the word, signifies that which the mind trows or believes to be fact or reality. It has its source in God, whilst knowledge proceeds from man. To be true, a proposition must be in exact accordance with what is or has been or shall be. Truth exists apart from the cognitions of the human mind. It would continue to exist if the mind of man were blotted out of existence, and there was truth long before the intelligence of man was called into being. The aim of thinking is to find out and lay hold of the truth. Thinking in which truth and error are mixed may have value as partial knowledge and as a stepping-stone to fuller knowledge. Knowledge becomes full and complete only in so far as it contains the truth, the whole truth, and nothing but the truth.
The ground of knowledge.
Full knowledge implies a basis upon which it may rest. There may be sufficient ground for the firm belief which constitutes the essence of knowledge even when the truth cognized is incapable of full and complete demonstration.
The reason why.
It is natural for a child to believe. The statements of others are accepted as true without question, so long as the child has not been deceived by others. Hence many teachers have assumed that their chief function is to ask the reason why, so that belief in what is true may be based upon sufficient ground, and that nothing shall be accepted as true until it is proved. This was one of the erroneous views under which Pestalozzi labored. He justified the undue attention paid to mathematics in his school on the ground that he wished his pupils to believe nothing which cannot be demonstrated as clearly as two and two make four. Whereupon Père Girard replied, “In that case, if I had thirty sons I would not intrust one of them to you; for it would be impossible for you to demonstrate to him, as you can that two and two make four, that I am his father and that I have a right to his obedience.”[47]
Exhaustive study.