The first of the Letters discusses the prejudices of mankind; the second, the heathen doctrine of immortality; the third, the origin of idolatry; while the fourth and fifth are devoted to Spinoza, the chief defect in whose philosophy is declared to be the absence of an explanation of motion. Motion belongs to the notion of matter as necessarily as extension and impenetrability. Matter is always in motion; rest is only the reciprocal interference of two moving forces. The differences of things depend on the various movements of the particles of matter, so that it is motion which individualizes matter in general into particular things. As the Letters ascribe the purposive construction of organic beings to a divine reason, so the _Pantheisticon_ also stops short before it reaches the extreme of naked materialism. Everything is from the whole; the whole is infinite, one, eternal, all-rational. God is the force of the whole, the soul of the world, the law of nature. The treatise includes a liturgy of the pantheistic society with many quotations from the ancient poets. Anthony Collins (1676-1729), in his _Discourse of Free-thinking_, shows the right of free thought _(i. e_., of judgment on rational grounds) in general, from the principle that no truth is forbidden to us, and that there is no other way by which we can attain truth and free ourselves from superstition, and the right to apply it to God and the Bible in particular, from the fact that the clergy differ concerning the most important matters. The fear that the differences of opinion which spring from freethinking may endanger the peace of society lacks foundation; on the contrary, it is only restriction of the freedom of thought which leads to disorders, by weakening moral zeal. The clergy are the only ones who condemn liberty of thought. It is sacrilege to hold that error can be beneficial and truth harmful. As a proof that freethinking by no means corrupts character, Collins gives in conclusion a list of noble freethinkers from Socrates down to Locke and Tillotson. Among the replies to the views of Collins we may mention the calmly objective Boyle Lectures by Ibbot, and the sharp and witty letter of Richard Bentley, the philologist. Neither of these attacks Collins's leading principle, both fully admitting the right to employ the reason, even in religious questions; but they dispute the implication that freethinking is equivalent to contentious opposition. On the one hand, they maintain that Collins's thinking is too free, that is, unbridled, hasty, presumptuous, and paradoxical; on the other, that it is not free enough (from prejudice).