It is of paramount importance to us human beings to discover an infallible criterion of what is true and what is false. What we seek is certainty. But where are we to find it?
We cannot derive it from our senses, for our senses deceive us, says Lamennais. That the senses conjointly correct such false impressions as each sense separately produces, is a fact of which he does not take cognisance. We are, in his opinion, the less certain of any necessary connection between the impressions of our senses and the reality of things, from our not even being certain of our own existence. How we, if we are not certain of that, can be certain of anything whatsoever, is a question he leaves unanswered.
Conviction, the inward feeling that the thing must be so, is, he affirms, as deceptive as are the impressions of the senses. The irresistible force with which a principle imposes itself upon our reason affords no proof of the truth of that principle. Error is always possible. That one may quite well acknowledge one's fallibility generally speaking, and yet regard one's self as certain of the truth in many single, definite cases, is another fact he leaves out of reckoning.
Next comes the turn of scientific research or reasoning. This, he maintains, leads to doubt of everything, for the highest of all principles do not admit of proof; we are not certain, moreover, of the reliability of memory. It is impossible to parry this attack upon the scientific method in so far that it is of course impossible to prove the reliability of memory without pre-supposing the reliability of the memory which is to be proved. But of the indirect proofs of the reliability of memory provided by human experience Lamennais does not say a single word.
He touches provisionally upon the subject of complete doubt. Complete doubt would lead to complete insanity. The spirit of self-preservation compels us to believe and to act according to our belief. It is, in the Abbé's opinion, this want of ability to doubt, or the knowledge that one will, if one doubts, be regarded by other men as ignorant or mad, which forms the foundation of all human certainty. Common consent (sensus communis) thus becomes for us the seal of truth, and there is no other. Difference of opinion at once begets uncertainty. A principle or a fact is more or less certain according as it is more or less universally accepted and borne witness to. Hence Lamennais' definition of a science is: A science is a collection of thoughts and facts on which all men are agreed. Though his standpoint is a different one, he resembles the English empirical philosophers of a later day in refusing even to such a science as geometry any foundation but that of common consent. The fact that many a mistaken scientific conclusion has been taken for truth is due, he believes, to the circumstance that science has reached only a small number of human beings. What, he exclaims, are a few hundred savants compared with the whole human race! He strangely enough forgets that the human race has never unanimously accepted a single scientific truth previous to its discovery by men of science, in fact has never shown original unanimity in any belief.
Lamennais asks: When two persons disagree, what do they do after they have in vain attempted to over-persuade one another? and he answers: They appeal to arbitration. But what is arbitration? Arbitration is authority, and this authority declares with which of the differing opinions certainty, or if not certainty, at least probability rests. The fact that the arguments of reason, as such, only create doubt, and the fact that the strongest proof of the mistakenness of an assertion always is: "You are the only one who thinks thus," direct us to the principle of authority as the only true and final principle.
Lamennais' theory, consistently developed, would lead to acceptance of the vote of the majority as the proof of truth. But our final destination is, as we know, the Catholic religion. It is interesting to follow the vaults by which the principle of authority, conceived of as it is in this work, carries us straight into the arms of the church.
Lamennais begins by defining all learning, all apprehension, as the obeying of an authority. This is the same as Bonald's theory, that we accept language upon the authority of those who teach us it, and accept along with it the truths which are necessary to self-preservation, truths which God in his all-powerful word (i.e. language) has revealed to every people upon earth. Our intellectual life, the law of which is obedience, is, then, simply a participation in the highest reason, a perfect harmony with the witness which the infinite being has borne of himself. Divine reason, which communicates itself by means of language, is the first cause of the existence of reasonable beings, and faith their necessary manner of being. Thus the principle of certainty and the principle of life are one.
Man being created for truth, the reason of universal humanity cannot err. Very different is it with the reason of the individual, which can be overwhelmed by doubt. If it separates itself from society it dies. Væ soli! exclaims Lamennais. The proud man imagines when he is required to bow to authority that what is demanded of him is that he shall yield up his reason. He is mistaken. Authority is simply universal reason, reason revealed through a witness. "It animates and preserves the universe which it has created. Without it no existence, no truth, no order."
It is, then, authority alone which gives us certainty concerning religion. "Religion is not only doctrine, not only systematised knowledge—it is also, it is essentially, a law." But there is no law without authority; these two ideas involve each other. Thus religion is necessarily based upon authority—the true religion upon supreme authority. It is defined as: "The sum of the laws which follow from the nature of reasonable beings;" and to learn what these are we must, consequently, have recourse to authority.