M. Jules Soury has said, in describing a certain type of mind: "Il est d'heureux esprits, des âmes fortes et saines, que n'effraie point le silence éternel des espaces infinis où s'anéantissait la raison de Pascal. Naïves et robustes natures, mâles et vigoureux penseurs, qui gardent toute la vie quelque chose des dons charmants de la jeunesse et de l'enfance même, une foi vive dans le témoinage immédiat de nos sens et de notre conscience, une humeur alerte, toute de joyeuse ardeur, et comme une intrépidité d'esprit que rien n'arrête. Pour eux tout est clair et uni; ou à peu près, et là où ils soupçonnent quelque bas-bond insondable, ils se détournent et poursuivent fièrement leur chemin. Comme cet Epicurien dont parle Cicéron au commencement du De natura deorum, ils ont toujours l'air de sortir de l'assemblée des dieux et de descendre des intermondes d'Epicure."
Such was Holbach. His philosophy is based on the child-like assumption that things are as they seem, provided they are observed with sufficient care by a sufficient number of people. This brings us at once to the very heart of Holbach's method which was experimental and inductive to the last degree. Holbach was nourished on what might be called scientific rather than philosophical traditions. As M. Tourneux has pointed out, he had been a serious student of the natural sciences, especially those connected with the constitution of the earth. These studies led him to see the disparity between certain accepted and traditional cosmologies and a scientific interpretation of the terrestrial globe and the forms of life which flourish upon it. Finding the supposed sacred and infallible records untrustworthy in one regard, he began to question their veracity at other points. Being of a critical frame of mind, he took the records rather more literally than a sympathetic, allegorical apologist would have done, although it cannot be said that he used much historical insight. After having studied the sacred texts for purposes of writing or having translated other men's studies on Moses, David, the Prophets, Jesus, Paul, the Christian theologians and saints, miracles, etc., he concluded that these accounts were untrustworthy and mendacious. He knew ancient and modern philosophy and found in the greater part of it an unwarranted romantic or theological trend which his scientific training had caused him to suspect. It must be admitted that however false or illogical Holbach's conclusions may be considered, he was by no means ignorant of the subjects he chose to treat, as some of his detractors would have one believe. His theory of knowledge was that of Locke and Condillac, and on this foundation he built up his system of scientific naturalism and dogmatic atheism.
His initial assumption is, as has been suggested, that experience (application réitérée des sens) and reason are trustworthy guides to knowledge. By them we become conscious of an external objective world, of which sentient beings themselves are a part, from which they receive impressions through their sense organs. These myriad impressions when compared and reflected upon form reasoned knowledge or truth, provided they are substantiated by repeated experiences carefully made. That is, an idea is said to be true when it conforms perfectly with the actual external object. This is possible unless one's senses are defective, or one's judgment vitiated by emotion and passion.
Holbach's contention is that if one applies experience and reason to the external universe, or nature, "ce vaste assemblage de tout ce qui existe"; it reveals a single objective reality, i. e., matter, which is in itself essentially active or in a state of motion.
From matter in motion are derived all the phenomena that strike our senses. All is matter or a function of it. Matter, then, is not an effect, but a cause. It is not caused; it is from eternity and of necessity. The cardinal point in Holbach's philosophy is an inexorable materialistic necessity. Nothing, then, is exempt from the laws of physics and chemistry. Inorganic substance and organic life fall into the same category. Man himself with all his differentiated faculties is but a function of matter and motion in extraordinary complex and involved relations. Man's imputation to himself of free will and unending consciousness apart from his machine is an idle tale built on his desires, not on his experiences nor his knowledge of nature. This imputation of a will or soul to nature, independent of it or in any sense above it, is a still more idle one derived from his renunciation of the witness of his senses and his following after the phantoms of his imagination. It is ignorance or disregard of nature then that has given rise to supernatural ideas that have "no correspondence with true sight," or, as Holbach expressed it, have no counterpart in the external object. In other words, theology, or poetry about God, as Petrarch said, is ignorance of natural causes reduced to a system.
Man is a purely natural or physical being, like a tree or a stone. His so-called spiritual nature (l'homme moral) is merely a phase of his physical nature considered under a special aspect. He is all matter in motion, and when that ceases to function in a particular way, called life, he ceases to be as a conscious entity. He is so organized, however that his chief desires are to survive and render his existence happy. By happiness Holbach means the presence of pleasure and the absence of pain. In all his activity, then, man will seek pleasure and avoid pain. The chief cause of man's misery or lack of well being is his ignorance of the powers and possibilities of his own nature and the Universal Nature. All he needs is to ascertain his place in nature and adjust himself to it. From the beginning of his career he has been the dupe of false ideas, especially those connected with supernatural powers, on whom he supposed he was dependent. But, if ignorance of nature gave birth to the Gods, knowledge of nature is calculated to destroy them and the evils resulting from them, the introduction of theistic ideas into politics and morals. In a word, the truth, that is, correct ideas of nature is the one thing needful to the happiness and well-being of man.
The application of these principles to the given situation in France in 1770 would obviously have produced unwelcome results. Holbach's theory was that religion was worse than useless in that it had inculcated false and pernicious ideas in politics and morals. He would do away completely with it in the interest of putting these sciences on a natural basis. This basis is self-interest, or man's inevitable inclination toward survival and the highest degree of well-being, "L'objet de la morale est de faire connaître aux hommes que leur plus grand intérêt exige qu'ils pratiquent la vertu; le but du gouvernement doit être de la leur faire pratiquer."
Government then assumes the functions of moral restraint formally delegated to religion; and punishments render virtue attractive and vice repugnant. Holbach's theory of social organization is practically that of Aristotle. Men combine in order to increase the store of individual well-being, to live the good life. If those to whom society has delegated sovereignty abuse their power, society has the right to take it from them. Sovereignty is merely an agent for the diffusion of truth and the maintenance of virtue, which are the prerequisites of social and individual well-being. The technique of progress is enlightenment and good laws.
Nothing could be clearer or simpler than Holbach's system. As Diderot so truly said, he will not be quoted on both sides of any question. His uncompromising atheism is the very heart and core of his system and clarifies the whole situation. All supernatural ideas are to be abandoned. Experience and reason are once for all made supreme, and henceforth refuse to share their throne or abdicate in favor of faith. Holbach's aim was as he said to bring man back to nature and render reason dear to him. "Il est tempts que cette raison injustement dégradée quitte un ton pusillamine qui la rendront complice du mensonge et du délire."
If reason is to rule, the usurper, religion, must be ejected; hence atheism was fundamental to his entire system. He did not suppose by any means that it would become a popular faith, because it presupposed too much learning and reflection, but it seemed to him the necessary weapon of a reforming party at that time. He defines an atheist as follows: "C'est un homme, qui détruit des chimères nuisibles au genre humain, pour ramener les hommes à la nature, à l'expérience, à la raison. C'est un penseur qui, ayant médité la matière, ses propriétés et ses façons d'agir, n'a pas besoin, pour expliquer les phénomènes de l'univers et les opérations de la nature, d'imaginer des puissances idéales, des intelligences imaginaires, des êtres de raison; qui loin de faire mieux connaître cette nature, ne font que la rendre capricieuse, inexplicable, et méconnaissable, inutile au bonheur des hommes."