In Defence of a Canon
In the field of art history, reference is often made to the "greatest" artists and works of a given medium/period. This begs the question: how does one make such evaluations, and why?
A canon is any group of things considered, by general consensus, to be the very best of their kind. The "canon of English literature", for instance, would include Shakespeare, Wordsworth, and Dickens.
The opinions of experts are crucial to the formation of a canon. It would take more than a lifetime to personally sift through all the surviving works of a single medium, from a single century. A canon is thus a massive collective effort.
It doesn't matter, of course, whether one's favourite works of art correlate with any canon. Nonetheless, canons are invaluable tools for art appreciation, as they provide students with excellent starting points for exploration. If one is curious about Baroque music, for instance, one can begin with the foremost works of Bach, Vivaldi, and Handel.
Moreover, a canon furnishes art lovers with common points of reference. A Baroque composer's compositional style, for instance, could be described in terms relative to Bach's. Thus does familiarity with the canon give rise to a universal vocabulary for art appreciation.
Finally, canons are useful for identifying the most influential artists of a given field. Even if one does not appreciate the works of Bach, one's understanding of music is enriched by awareness of his influence on subsequent composers.
In short, canons serve as sturdy frameworks upon which a fulfilling art education may be constructed.