In the 17th century.

The new concern with Skepticism was given a general philosophical

formulation by Michel de Montaigne and his cousin Francisco Sanches. Montaigne in Apology for Raimond Sebond and Sanches in Quod nihil scitur, both written in 1576, explored the human epistemological situation and showed that man's knowledge claims in all areas

were extremely dubious. Montaigne recommended living according to nature and custom and accepting whatever God reveals, and Sanches advocated recognizing that nothing can be known and then trying to gain what limited information one can through empiric al scientific means.

Montaigne's Skepticism was extremely influential in the early 17th

century. His followers, Pierre Charron, J.-P. Camus, La Mothe Le Vayer, and others, further popularized his views. Various French Counter-Reformers used the arguments of Montaigne and Sextus to undermine Calvinism. Montaigne's Skepticism opposed all so rts of disciplines, including the new science, and was coupled with a fideism that many suspected to be insincere.

In the 1620s efforts to refute or mitigate this new Skepticism appeared. A Christian Epicurean, Pierre Gassendi, himself originally a Skeptic, and Marin Mersenne, one of the most influential figures in the intellectual revolution of the times, while retaining epistemological doubts about knowledge of reality yet recognized that science provided useful and important information about the world. The constructive Skepticisms of Gassendi and Mersenne, and later of members of

the Royal Society of England like Bishop John Wilkins and Joseph

Glanvill, developed the attitude of Sanches into a hypothetical, empirical interpretation of the new science.

Rene Descartes offered a fundamental refutation of the new Skepticism, contending that, by applying the skeptical

method of doubting all beliefs that could possibly be false (due to

suffering illusions or being misled by some power), one

would discover a truth that is genuinely indubitable, viz., "I think,

therefore I am" (cogito ergo sum), and that from this truth one could discover the criterion of true knowledge, viz., that whatever is clearly and distinctly conceived is true. Using this criterion, one could then establish: God's existence, that he is not a deceiver, that he guarantees our clear and distinct ideas, and that an external world exists that can be known through mathematical physics. Descartes, starting

from Skepticism, claimed to have found a new basis for certitude and for knowledge of reality. Throughout the 17th century Skeptical critics--Mersenne, Gassendi, the reviver of Academic philosophy Simon Foucher, and Pierre-Daniel Huet, one of the most learned men of the age--sought to show that Descartes had not succeeded, and that, if he sincerely followed his skeptical method, his new system could only lead to complete Skepticism. They challenged whether the cogito

proved anything, or whether it was indubitable; whether Descartes' method could be successfully applied, or whether it

was certain; and whether any of the knowledge claims of Cartesianism were really true. Nicolas Malebranche, the developer of occasionalism, revised the Cartesian system to meet the Skeptical attacks only to find his efforts challenged by the new Skept ical criticisms of Foucher and by the contention of the Jansenist philosopher Antoine Arnauld that

Malebranchism led to a most dangerous Pyrrhonism.

Various English philosophers culminating in Locke tried to blunt the

force of Skepticism by appealing to common sense and to the "reasonable" man's inability to doubt everything. They

dmitted that there might not be sufficient evidence

to support the knowledge claims extending beyond immediate experience. But this did not actually require that everything

be doubted; by using standards of common sense, an adequate basis for

many beliefs could be found. Blaise Pascal, who presented the case for Skepticism most forcefully in his Penses, still denied that there can be a complete Skepticism; for nature prevents it. Lacking rational answers to complete Skepticism, man's only recourse lies in turning to

God for help in overcoming doubts.

The culmination of 17th-century Skepticism appears in the writings of

Pierre Bayle, especially in his monumental Dictionnaire historique et critique (1697-1702). Bayle, a superb dialectician, challenged philosophical, scientific,

and theological theories, both ancient and modern, showing that they all led to perplexities, paradoxes, and contradictions.

He argued that the theories of Descartes, Spinoza, Leibniz, and

Malebranche, when skeptically analyzed, cast in doubt all

information about the world, even whether a world exists. Bayle

skillfully employed Skeptical arguments about such things

as sense information, human judgments, logical explanations, and the

criteria of knowledge in order to undermine confidence in human intellectual activity in all areas. Bayle suggested that man should abandon rational activity and turn blindly to faith and revelation; he can therefore only follow his conscience without any criterion for determining true faith. Bayle showed that the interpretations of religious knowledge were so implausible that even the most heretical views, like Manichaeism, known for its cosmic dualism of good and evil, and Atheism, made more sense. A s a result Bayle's work

became "the arsenal of the Enlightenment," and he was regarded as a major enemy of religion.