In June 1970, a reluctant Bob Dylan turned up at Princeton University to receive an honorary degree. He had been persuaded to attend by his then-wife, Sara, and his friend and fellow musician David Crosby, but the ceremony so rattled him that he referred to it subsequently in a scathing song called Day of the Locusts. It included the line, “sure was glad to get out of there alive”.

What annoyed Dylan most was the introductory speech in which he was referred to as “the disturbed and concerned conscience of young America”. Over three decades later, as the following passage from his 2004 memoir, Chronicles Volume One, illustrates, that description still rankled. “Oh sweet Jesus! It was like a jolt. I shuddered and trembled but remained expressionless. The disturbed conscience of young America. There it was again. I couldn’t believe it! The speaker could have said many things, he could have emphasised a few things about my music.”

Early on in Why Dylan Matters, Richard F Thomas, a classics professor at Harvard, recalls the Princeton incident before setting out to emphasise a few new things about Dylan’s music, as if to make amends for the careless words that so offended his subject. Academics have picked over Dylan’s songs in the past, most notably the Cambridge don Christopher Ricks, who made heavy work of the myriad allusions therein in his grandly titled Dylan’s Visions of Sin. In the wake of the Nobel prize in literature controversy, Thomas’s timely book goes further by attempting, though not always convincingly, to recast Dylan as an heir to Virgil and Homer. “He is part of that classical stream,” asserts Thomas, “whose spring starts out in Greece and Rome and flows on down though the years...”

This may be so, but in affixing Dylan’s songwriting to that Graeco-Roman tradition, Thomas is forced to constantly negotiate a line between the scholarly and the tenuous. We learn, for instance, that the young Robert Zimmerman liked Hollywood-produced cod-Roman epics as a boy and was briefly a member of his school’s Latin club. How much this proves a deep and abiding affinity with the classics is debatable. Likewise, the number of times that Dylan has included Rome on his touring schedule is hardly evidence of the same given that Dylan tours the world’s capitals constantly.

Thomas also cites the relatively minor Dylan song When I Paint My Masterpiece as further evidence of Dylan’s love for, and identification with, Rome. One can only wonder what the singer’s poetic predecessors would have made of lines as throwaway as the opening verse: “Oh, the streets of Rome are filled with rubble/ Ancient footprints are everywhere/ You can almost think that you’re seein’ double/ On a cold, dark night on the Spanish Stairs...” Ovid it ain’t.

Thomas is more persuasive when he looks at Dylan’s work in light of the other many influences the singer draws on, which range from 19th-century symbolist poetry to early American folk and blues by way of Woody Guthrie, Hank Williams, Chuck Berry, the Beat poets and the Bible. Dylan is nothing if not wide-ranging in his inspirations.

The book is oddly structured, the autobiographical fandom of the first chapter and a recollection of an academic symposium he attended in Dylan’s home town of Hibbing, Minnesota, soon giving way to a series of intermittently illuminating reflections on various subjects: selected albums, the memoir, the Nobel prize literary canonisation, as well as the accusations of plagiarism that have periodically dogged Dylan. One of the most revealing sections concerns Dylan’s creative “stealing” from Ovid for his Modern Times album. “It eventually emerged,” writes Thomas, “that more than 30 lines of Ovid’s exile poems had been reappropriated and become an essential part of the fabric of the songs...” Thomas is surprisingly forgiving of such widespread borrowing, describing it as transformative and praising Dylan for bringing these “long-dead souls” back to life and “in effect bringing them into the modern times”.

For all that, there is a definite suggestion of intellectual snobbery in Thomas’s choice of title: Why Dylan Matters. It is echoed, too, in his fellow classical scholar, Mary Beard’s assertion on the book cover: “At last an expert classicist gets to grips with Bob Dylan.” Both suggest, unconsciously or otherwise, that Dylan’s songwriting only really matters if he can be shoehorned into the Homeric tradition and that academic canonisation is the ultimate vindication of Dylan’s worth. It isn’t. Nor, even, is the award of the Nobel prize in literature.

What is worth remembering here is that Dylan is a singer-songwriter who uses classical poetry in much the same way that he uses old blues and folk songs: as raw material for songs that only occasionally stand up to the kind of scholarly scrutiny that complex poems can withstand. Revealingly, there is little here about how Dylan delivers his songs, the emotional thrust of that imperfect, now faltering, voice and his often wilfully perverse delivery. One could argue that the majority of Dylan’s songs evade academic interpretation, that they come to life when performed rather than as texts on the page.

In this context, Why Dylan Matters misses the point, but there are nevertheless enough glimpses of illumination to make this a must for the converted. The rest of us can enjoy the songs without carrying the burden of how to measure or fully explain them, buoyed by Dylan’s own admission in his Nobel prize acceptance speech: “Not once have I ever had the time to ask myself: ‘Are my songs literature?’”

• Why Dylan Matters by Richard F Thomas is published by William Collins (£12.99). To order a copy for £11.04 go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99