All you need to know about the books you meant to read

Chaucer's late masterpiece is a collection of verse fictions written in a protean array of styles and genres. One hundred and sixteen were planned, but only 23 completed.

Plot: In the General Prologue, the poet presents himself as an observant bore travelling with a group of ''sundry folk by aventure (chance) yfalle / In felaweship'' on a pilgrimage to Becket's shrine in Canterbury.

The innkeeper Harry Bailly suggests that, to keep themselves amused, the pilgrims, who are both socially representative and a rag-bag, should swap stories - and the most edifying or entertaining will earn a free meal.

Each tale reflects upon the character of the teller. The ''parfit gentil'' knight tells the first and longest:a highly patterned courtly narrative of two friends who fall in love with the same girl, which is resolved with the death of one of the lovers in an elaborate tournament. The Miller then presents his own idiosyncratic version of the ''two boys and a girl'' theme, except that his tale ends not in death but with a hot iron up the bottom. The pilgrims continue their exchange of noble, smutty, religious stories as Harry Bailly struggles to maintain an aesthetic and social cohesion.

The sequence ends with the parson's serious exposition of God's purpose as revealed by Christian theology. As the Parson examines the Seven Deadly Sins, the reader is forced to reconsider the pilgrims and the nature of their ultimate destination.

Theme: The pilgrimage of life. Pride, avarice, anger, lust etc hinder our progress towards salvation. Conversely, sin makes people different from each other, makes them human, and therefore more fitting for God's grace. Chaucer's comedy is his tolerant recognition of humanity's failings; his irony is the realisation that humanity's earthly aspirations are absurd.

Style: The rhyming pentameters encompass with equal facility both the stilted properties of the Prioress and the rougher expressive powers of the Summoner and the Friar. Chaucer is astonishingly versatile. He can wield an epic simile as deftly as he can blow a raspberry.

Chief strengths: Chaucer used every available form: bawdy fabliau, courtly romance, beast fable, sermon, epic, saint's life ... No poem in the language shows such variety coupled with such white-knuckled intellectual grip. Despite working within the enclosed system of Christian doctrine, Chaucer does not indulge in praise or blame. The final judgement will come from God and the reader who rushes to condemn is tripped by the webs of irony.

Chief weaknesses: The harsh realities of disease and poverty are excluded from Chaucer's picture of medieval life; Langland's long poem Piers Plowman has the advantage here.

What they thought of it then: Chaucer's fellow poets (now sunk into oblivion) rattle with praise. Lydgate called him ''my master'', Hoccleve believed him ''the first finder of our fair language''.

What we think of it now: Political, feminist and theological analyses are loosening the ''merrie England'' cosiness that has stifled Chaucerian studies.

Responsible for: The stabilising of the English language and the creation of the very idea of "English literature''.