"There are more things in heaven and earth, Horatio," says Hamlet, "Than are dreamt of in your philosophy) -- and so it is, many people would add today, with philosophy in general. What used to be viewed as the quest for truth is now more often seen as a kind of gray war of the obscure versus the narrow. Philosophy's reputation for obscurity has its source in the turgid prose of German thinkers like Kant, Hegel and Heidegger, while the charge of narrowness is often leveled against analytical philosophers in the tradition of David Hume, Bertrand Russell and G.E. Moore.

Philosophers may defend themselves by pointing out that the public perception (or rather misperception) of philosophy as obscure or narrow is attributable to the subject's inherent difficulty. This defense, however, while containing a valid point, does not really address the issue. For it is not the difficulty of philosophy that people resent so much as what they judge to be its lack of relevance. The philosopher today is thought of less as a "lover of wisdom" than as what Plato called a "philodoxer," a lover of opinion. The exasperation and impatience he is capable of arousing -- in other philosophers as well as non-philosophers -- was comically noted by the 20th-century philosopher Ludwig Wittgenstein: "So in the end when one is doing philosophy one gets to the point where one would like just to emit an inarticulate sound."

Hill and Wang's new Past Masters series should elicit relatively few inarticulate sounds. The series, of which the first six volumes are surveyed here, combats the prevalent image of philosophy as obscure or narrow in two important ways. First, the series deals with substantial philosophical issues without becoming too technical or abstruse. Each small volume of about 100 pages, written by a distinguished contemporary scholar, considers, from a broadly intellectual standpoint, the contributions of one of Western civilization's major humanists, scientists or religious figures.

The second way in which this series defends the honor of this oldest of intellectual disciplines is through the wide-ranging nature of its selections. Though the works on Jesus and Dante may strike some readers as incongrous in a series devoted to leading "intellectual" figures of the past -- both books take note of this apparent incongruity -- their inclusion in fact only manages to convey, without doing violence to the provinces of religion and poetry, a sense of philosophy's potential breadth.

The general approach of Humphrey Carpenter's book, a sensitive and perceptive analysis of "the teachings" of Jesus, is to compare what Jesus said as reported in the Gospels with the dominant views of the Judaism of his time. The picture that emerges is one of Jesus as something of a moral revolutionary, though Carpenter is careful to emphasize that Jesus was engaged not so much in breaking traditional Jewish law as intensifying its character. "Do not suppose that I have come to abolish the Law . . . ," Carpenter quotes from Matthew's Gospel. "I did not come to abolish, but to complete." Unlike many such studies, Carpenter's manages to convey this sense of Jesus's "completion" -- the wholeness of his life, thought and character.

With the medieval figures Dante Alighieri (1265-1321) and Thomas Aquinas (1225-1274), such "wholeness" shows of breaking into parts; both men inhabited a world in which a conflict between reason and faith was emerging. Dante's effort to resolve this conflict, as George Holmes points out in his book, drew heavily on the Neoplatonism of his day -- that is, the doctrine that postulates a single source (the One) from which all forms of existence emanate and with which the soul seeks a mystical union. Holmes devotes the majority of his book to an analysis of Dante's Divine Comedy , skillfully weaving together in the process an account of the poet's personal life and his rather unmodern, Neoplatonic world view.

In the thought of Thomas Aquinas, on the other hand, the Neoplatonic influences are greatly dimished and more modern (though still definitely medieval) philosophical tendencies appear. The philosophy of the Dominican friar (who was made "the official theologian" of the Roman Catholic Church in the 19th century) is usually presented as an effort to merge the Aristotelian and Christian world views into an harmonious whole. Anthony Kenny's philosophical, mostly nonhistorical treatment of this "merger" is both inspiring and not very good. It is not very good because the discussion (unlike that of its companion volumes) is so sophisticated as to make much of the book inaccessible to anyone who does not have some prior knowledge of this very difficult philosopher. But it is alos inspiring in the use it makes o Wittgenstein's thought to interpret Aquinas. As Kenny notes, adherence to traditional philosophical categories of thought (i.e. those associated with the French philosopher Descartes) has caused contemporary philosophers generally to exclude Aquinas from sustained and serious philosophical consideration. With Wittgenstein's overthrow of these categories -- and the tremendously liberating effect the works of his later peiod have had in general -- this situation (Kenny clearly hopes) will change. His book, which closes by citing a favorable reference of Wittgenstein's to Aquinas, may itself help to promote that change.

With Pascal, Hume and Marx, one enters into a more modern period in which the predominant tendency is not so much to reconcile what are perceived to be the two opposing forces of faith and reason, but to drive them further apart. Blaise Pascal (1623-1662), a religious thinker and mathematician of genius, is well-known for his insistence on faith's primacy over reason. As Alban Krailsheimer notes in his extremely fine account of Pascal's life and work, however, Pascal's denial of "the rights of reason" has been exaggerated and in any case entailed not only an acceptance of the authority of scripture in matters of faith, but an acceptance of the authority of the senses in matters of fact. The author of Pensees was a scientist as well as a mathematician and, as Krailsheimer puts it, "absolutely rejected the idea that reason alone was the way to truth in theology or the physical sciences."

But if Pascal repudiated to a large extent the rationalism of his time, the English analytical philosopher David Hume (1711-1776) undermined its foundations in a much more radical way. Without having recourse to religious faith, and basing his analysis heavily on the empiricist dictum that all knowledge is derived from "impressions," the immediate date of experience, Hume came to the conclusion that our beliefs in the self, causality and the external world were without rational justification and could be accounted for only by custom, habit and the psychological processes associated with them. Hume did not mean to imply by this argument that we should abandon such beliefs, as A.J. Ayer (himself a leading contemporary analytical philosopher) notes in his book; rather, Hume's point was that we have no basis in reason for them.

Like Hume, Ayer is an excellent writer, and his account of Hume's philosophy is lucid, absorbing and, within limits, critical. I say "within limits" because although Ayer criticizes (and corrects) what he regards as the deficiencies of Hume's analysis, such criticism at no point challenges Hume's fundamental perspective, which entailed a severing of the spheres of philosophy and everyday life.

Such a challenge can be found in the writings of Karl Marx (1818-1883). In sharp contrast to Hume's ironic and detached manner, Marx declared stirringly: "The philosophers have only interpreted the world in various ways; the point is, to change it." Marx did not mean by this assertion that philosophy was unimportant, as Peter Singer observes in his clear, simplified account of Marx's views; rather, he meant that philosophy should have a more active role than past philosophers had given it. Philosophy in Marx's view could transform the world by helping to rid it of the disease of capitalism; its proper role was in this sense curative.

Many philosophers today, of course, see Marx's "cure" as a deadly one, based not only on a naive view of history as purposive but on a dangerous conception of human nature as malleable. Nonetheless, it is Marx, more than any other thinker in the last century and a half, whose life and work testify to the power of philosophy.