SAINT PATRICK'S, one of Dublin's two Anglican cathedrals, a 12th-century foundation with extensive and not always happy modern "restorations," stands on the south bank of the Liffey, surrounded by what once were elegant 18th-century buildings but now are slums. In summer, busloads of tourists, dogged and glad to be out of the Dublin drizzle, are led down the aisles. High above them, tattered, faded and dusty are the flags and battle honors of imperial wars. But other visitors have a different objective in mind, and it leaps out at them suddenly, above the door to the robing-room.

It is, of course, Jonathan Swift's great epitaph, "deeply cut and strongly gilded," upon a tablet of black marble. Hic depositum est . . . it begins: "Here lies the body of Jonathan Swift, Doctor of Divinity and Dean of this Cathedral Church, where savage indignation can no more lacerate his heart. Go, traveller, and imitate if you can one who strove with all his might to champion liberty."

With Swift, everywhere we turn there are puzzles, uncertainties, ironies, and not least those inscribed, by his direction, upon the plaque. We have never been certain of the source or direction of that saeva indignatio, while never doubting its existence. And we know, as though upon instinct, as though that extraordinary prose, neat and ferocious, had enforced the knowledge on us, that he was a champion, in some way or other, of liberty. But what way?

At the end of his life, the Dublin crowds hailed him as a patriot, as their champion, as indeed he was, as his pamphlets on behalf of Irish rights testify. But he held those crowds in disdain, and clung constantly to his birthright as an Englishman, descendant of the English colony. Not, surely, a champion of religious liberty, in the ordinary meaning of that term, for the majority of the Irish were either Catholic or Presbyterian, and he distinguished between these sects only to the degree that he detested the Presbyterians and despised the Catholics. Certainly he supported to the hilt the civil disabilities under which they labored in his century.

Puzzles as to what Swift actually believed and felt have found a curious reflection in uncertainties as to his biography, and especially in his relationship to the two women who have come down to us by the names he bestowed upon them, "Stella" and "Vanessa," Esther Johnson and Hester Vanhomrigh. The full outlines of these relationships will never be known, although David Nokes (unlike Irwin Ehrenpreis, Swift's most recent earlier biographer) thinks that a marriage with Stella was at least possible, and perhaps likely.

Swift has attracted extraordinary biographers -- Johnson, Scott, Thackeray, and a host of memoirists who early on, in some instances before his death, set down their accounts of his character and conversation, rightly confident that he was a man and writer of rare genius, however baffling and baffled. That first generation of memoirists created legends which, on the whole, Scott and following him, Thackeray, accepted. It is thus, for example, that Scott, following the account given by Tom Sheridan, made current the vivid and unforgettable account of Swift's furious ride to Celbridge, to break off relations with "Vanessa" by flinging down, wordlessly, her calamitous letter to "Stella."

SIMILARLY, in the last years of Swift's life, when his mental faculties had failed him, he fell under the judgment of a Commission of Lunacy. The legend grew that his servants took money to show him to the curious. "And Swift expires," as Doctor Johnson was to put it, "a driveller and a show." But this, as Nokes says, "seems too neatly ironic an example of the teagues and yahoos taking their revenge on the man who scourged them. It is surely ironic enough that Swift, whose last 'satiric touch' was to bequeath a lunatic asylum to Dublin, should have spent the last three years of his life under the care of guardians appointed by a Commission of Lunacy."

In the present century, scholars have been briskly and exhaustively at work clearing away this undergrowth of legend, a task which culuminated in Ehrenpreis' massive three-volume biography, of which the first was published in 1962 and the third 21 years later. The legends vanished beneath his searching pen, but so, for me at least, did Swift himself, his outlines obscured by thick coatings of academese. The dust jacket of Nokes' biography says that it should "long remain the standard, one-volume biography of Swift for all students and general readers." For once a blurb is too modest. By contrast, Ehrenpreis has composed a monumental biography. For anyone in search of an even-handed evaluation of contending theories as to the meanings of The Tale of a Tub or of the political and theological issues of Swift's day, Ehrenpreis is irreplaceable.

Nokes too is a searching scholar, although he wears his learning rather more lightly, which would probably have pleased Swift -- with Swift, you never know. But he has done something more than scholarly -- he has created, for the first time, a coherent and illuminating portrait of a great writer and tormented man, in whom coherence itself was often a distracting mask. It is not easy to move from an examination of Swift's complex and ambiguous Discourse of the Contests and Dissensions in Athens and Rome to an unsparing and unshocked account of his "familiar obsessions with cleanliness, thrift, and the operations of the bowels." And it is all too easy to want to explain the one in terms of the other: to reduce much of what is terrifying and disturbing in Swift to the status of neurotic symptoms. But Nokes is never reductive; he has his own sense of the ultimate unfathomability of what we used to call the soul.

Of the terrible in Swift, there can be no doubt. Thackeray, discussing him before a respectable Victorian lecture audience said: "As fierce a beak and talon as ever struck. I am glad, for once, that fate wrested the prey out of his claws, and cut his wings and chained him. One can gaze, and not without awe and pity, at the lonely eagle chained behind the bars." It is a powerful but slightly fuzzy metaphor: what, after all, was Swift's prey? His letters and what we know of his conversation to one side, in the most famous of his political writings he was, almost invariably, defending the weak against the strong. But the awe which Thackeray speaks of was genuine: it was the awe which everyone who writes in English feels in the presence of that magnificent prose.