More specifically: deCopia is an online database that names, describes, and thoroughly exemplifies the patterns of syntax and style that make certain specimens of English especially interesting, effective, beautiful, and unique.
For most people (who aren't linguists, rhetoricians, or professors of literature), deCopia is a reference that offers a new way to think about language. Instead of focusing on what is said (as in a quotation collection) or on what words mean (as in a dictionary) or on the overall structure of arguments (as in a college-level composition textbook), deCopia focuses on how sentences and paragraphs are crafted—the endlessly varied patterns we form in our efforts at expression and communication.
Eggheads since Aristotle have known that well-crafted statements can be anatomized and classified according to how they work, why they work, what they do that distinguishes them from other expressions of similar ideas; and that this analytical process, followed-up with deliberate imitation, can help us to improve our command of language. At deCopia, you'll find sentences, paragraphs, and slightly longer passages tagged according to their distinctive qualities—using the terminology of grammar, rhetoric, and literary criticism—so that you, the curious learner, can browse explanations and examples of distinctive stylistic patterns, delight in their aesthetic variety, consider their discursive effects, even imitate and manipulate choice devices until you make them your own. As long as a language pattern can be named, consistently identified, and exemplified—and interests somebody, for whatever reason—it deserves a place in deCopia.
De Ultraque Verborum ac Rerum Copia—translated as Copia: Foundations of the Abundant Style and abbreviated as De Copia—is a manual of rhetoric by the famed Renaissance scholar and early humanist Desiderius Erasmus. In it, Erasmus explains, analyzes, and exemplifies the rhetorical virtue of copiousness, or abundance: that is, the speaker or writer's command over a wide variety of expressive possibilities.
In one famous chapter, Erasmus comes up with 195 different ways to say "Your letter pleased me greatly," intending to show that each variation in his parade manifests different virtues appropriate to different circumstances; and that the masterful stylist, fertile and adaptable, is able to employ the right one at the right time.
Like most other books on rhetoric, Erasmus' work had two primary aims: to analyze and to educate. Traditional scholars of rhetoric classified language patterns in order to understand and explain how and why well-crafted expressions achieve their ends; then they presented terminology and models that could help language-users (from schoolboys to professional rhetoricians) improve the variety and control of their style and, as a result, the power of their statements. deCopia aims to do the same.