In June 1663 Spinoza moved from Rijnsburg to Voorburg, near The Hague. Here Spinoza got to know Vossius the philologist, who was subsequently appointed Canon of Windsor, and Christiaan Huygens, the discoverer of Saturn's rings, inventor of the pen dulum clock, and originator of the undulatory theory of light.
Though busy with his Ethics and his lenses, Spinoza kept up his correspondence with various people, especially with Olden burg. Oldenburg kept Spinoza informed of the doings of the Royal Society (which had obtained its charter in July 1662) and of the researches of Robert Boyle and others, and solicited news from Spinoza about Huygens and others. But about 1665 the correspondence was interrupted. The Great Fire of London (1666) and the continuation of the war were no doubt responsible for this. In 1667 Oldenburg was suspected of espionage and clapped into the Tower of London for a time. He was released, but became nervous and cautious, so that his correspondence with Spinoza was not resumed until 1675.
From a letter written in June 1665 it appears that Spinoza was then 'nearing the completion of his Ethics ( Correspondence, p. 202). In the following August or September, however, Spinoza informed Oldenburg that he was engaged on a theological treatise (see Correspondence, pp. 204, 206). During the next few years Spinoza was at work on his Tractatus Theologico-Politicus, which was published anonymously in 167o. Why did he put aside his Ethics in order to write a treatise on the Scriptures? The chief reason is stated on the very title-page of the Tractatus, which states that its object is "to show that not only is perfect liberty to philosophize compatible with devout piety and with the peace of the State, but that to take away such liberty is to destroy the public peace and even piety itself." Already in 1665 Spinoza mentioned this object to Oldenburg. But he also mentioned another, namely, he wanted to clear himself of the charge of atheism which had been brought against him. It would appear that, with the completion of the Ethics in sight, Spinoza was considering the question of its publication, but found that such a step was impracticable in the then state of public opinon, which under the increasing influence of the clerics and monarchists became very intolerant and restive, as the troubles caused by the war multiplied. Spinoza consequently conceived the plan of vindicating the cause of freedom of thought in a manner that would at once serve the general interest of the Republic and also prepare the way for the publication of his own philosophy. The chief obstacle was the Calvinist clergy with their constant appeal to Scripture, which they interpreted in any manner that served their fanaticism. So Spinoza set himself the task of showing that the Bible, properly understood, gives no support to the intolerance of the clerics and their interference in civil and political affairs. Last Years (167o-1677).—In May 167o, shortly after the anonymous appearance of the Tractatus Theologico-Politicus, Spinoza moved into The Hague, possibly in order to be nearer some of his influential friends. He certainly needed protection.
His book created a stir, and went through five editions in as many years. But it stirred a hornet's nest, and denunciations came fast and furious. At first Spinoza stayed on the Stille Veer kade, but in 1671 he went to stay with the Van der Spycks in the Paviljoensgracht near by, and remained in their house (now Domus Spinozana) to the end of his days. His work on the Tractatus involved the resumption of his earlier Hebrew studies, and it was about this time that he commenced his Hebrew Gram mar. He did not, however, finish it, but returned to his Ethics, though the prospect of its publication became more and more remote. In 1672 the French invaded Holland, which was unpre pared, and so suffered many disasters. The populace, fomented by the monarchists, sought a scapegoat, and murdered the brothers Jan and Cornelius de Witt. Spinoza was beside himself. He pre pared a placard expressing his disgust with "the very lowest of barbarians," and was going to post it up on the scene of the crime. Fortunately Van der Spyck locked the door, and saved him from the fate of the De Witts. As it was, his Tractatus was denounced as an instrument "forged in hell by a renegade Jew and the devil, and issued with the knowledge of Mr. Jan de Witt." In 1673, while the French army was at Utrecht, Spinoza received an invitation to visit Prince Conde there. It was inspired by a Colonel Stoupe, who was in command of a Swiss regiment under Conde. Stoupe had been a Calvinist minister, and his service with Catholic France against Calvinist Holland evoked the severe censure of some of his countrymen. Stoupe was an unscrupulous adventurer, but was anxious to save appearances. So he con ceived the idea of showing that the Dutch were really heretics, and for this purpose he wanted to use Spinoza as his cat's paw. He actually published later in that year a little book in which he denounced the Dutch for tolerating an atheist like Spinoza, and for making no attempt to answer his atheistical treatise. Spinoza only saw in the invitation a possible opportunity of initiating peace negotiations. So he consulted some people of authority, and, armed with the necessary safe-conducts, set out for Utrecht in May 1673. In the meantime Conde had been called away, and Spinoza after waiting for him several weeks in vain, returned to The Hague, where a suspicious rabble greeted him with scowls and stones, but did him no harm. Earlier in the same year another kind of invitation had reached Spinoza. It was an invitation from the Elector Palatine to the Chair of Philosophy in the University of Heidelburg. Spinoza declined the offer with many thanks. He had trouble enough with the clerics and theologians as a recluse, he would not court worse trouble by becoming a public character. So he stayed in The Hague, polishing his Ethics and his lenses, and generally prac tising the art of plain living and high thinking. The impression he made on the people about him may be gathered from the fact that one day his pious Lutheran hostess asked him whether he considered her religion the right way to salvation. Spinoza, of course, reassured her.