Was he a Catholic? A conforming Anglican? Or could he even have been an atheist, as Gary Sloan recently suggested in the Freethinker? The answer, surely, is that while he was a believer, a liberal Christian, Shakespeare has all the characteristics of a Renaissance humanist. He was a man of the highest culture and a great familiarity with the classics, which are of central importance in the plays and in the structure of his imagination.

The works are saturated with his favourite classical authors, especially Ovid, Virgil, Seneca, Plautus, Cicero, Terence and Plutarch. Indeed, he has the ancient mythology and history at his finger tips. He also shared the Renaissance desire to seek the truth about human nature. The ancient adage nosce teipsum – know thyself – was a key principle of humanist thought, and Hamlet's speech about holding the mirror up to nature implies that poetry and drama can help us to acquire that wisdom. By doing so, we can better guard against the barbarism lurking below the surface which the baser side of human nature creates and instead promote the more civilised values.

As Robin Headlam Wells writes in Shakespeare's Humanism, his plays betray their humanist origins in the themes they dramatise: "Repeatedly, they come back to those matters that concern Duke Vincentio in Measure for Measure: 'the properties of government', 'our city's institutions', 'the terms for common justice', 'the nature of our people'."

At first glance, his humanism seems close to the disillusioned brand of Montaigne, who stressed the limitations of reason and understanding in human affairs, in contrast to the optimism of Bacon, Erasmus and most other Renaissance writers, who believed that cultivating reason would lead to a better understanding of how to act and thus to great benefits for society as a whole. Shakespeare's apparent scepticism about such matters is exemplified in Hamlet's famous speech: "What a piece of work is a man! How noble in reason! How infinite in faculty! In form and moving how express and admirable! In action how like an angel! In apprehension how like a god! The beauty of the world! The paragon of animals! And yet, to me, what is this quintessence of dust?" (Act II, Scene II). This appears to be a counterblast to Pico della Mirandola's Oration on the Dignity of Man, sometimes called the 'manifesto of the Renaissance,' which argues for the dignity and, even, potential divinity of man.

Yet this is hardly the full picture. Hamlet, in the early part of the play, is a confused and disillusioned idealist. But he matures as he grows older. Ultimately the play challenges Hamlet's early cynicism. Similarly, Shakespeare himself shows progression from the tragedies to the late romances, where the message is quintessentially humanist.

Prospero in The Tempest is a metaphor for the civilising power of the artist and educator whose 'liberal arts' tame the tempests in the human spirit. He exhibits the ennobling qualities of compassion, generosity, friendship and wisdom. He does not seek to retaliate against those who wronged him; he seeks only to bring them out of the darkness of hatred and revenge. Like many Renaissance humanists, Shakespeare had a sceptical outlook and delighted more in presenting issues than in espousing systems. He held critical awareness, as opposed to doctrinal rectitude, to be the highest possible good.

This is precisely what Keats called 'negative sensibility' in which the author is content and proud to be in a state of doubt. His works are deliberately dialectical and provisional: they dramatise the unresolvable tensions that are the fundamental conditions of life. This led to him being often misunderstood: Dr Johnson famously lamented that "he sacrifices virtue to convenience, and is so much more careful to please than to instruct that he seems to write without any moral purpose." Yet Johnson forgets the Renaissance habit of instructing by pleasing. Overall Shakespeare's unparalleled realism may be seen as the ultimate embodiment, in poetic terms, of the intense concern for specificity endorsed by humanists from the 14th century on.

Shakespearean drama is a treasury of the disputes that frustrated and delighted humanism, including (among many others) action versus contemplation, theory versus practice, art versus nature, res versus verbum, monarchy versus republic, human dignity versus human depravity, and individualism versus communality. In treating of these polarities, he generally proceeds in the manner of Castiglione and Montaigne, presenting structures of balanced contraries rather than syllogistic endorsements of one side or another. In so doing, he achieves a higher realism, transcending the mere imitation of experience and creating, in all its conflict and fertility, a mirror of mind itself.

Since the achievement of such psychological and cultural self-awareness was the primary goal of humanistic inquiry, and since humanists agreed that poetry was an uncommonly effective medium for this achievement, Shakespeare must be acknowledged as a pre-eminent humanist.