How does a canon differ from a fugue?

While both the canon and the fugue are foundational techniques in Western polyphony based on the principle of imitation, they differ significantly in their structure and evolution.1

• Canon: This is the most rigorous form of imitative technique, where an initial melody is imitated by one or more parts at a specified time interval. In a strict canon, each successive voice plays or sings the exact same melody, sometimes utilizing techniques like augmentation, diminution, or inversion.21
• Fugue: A fugue is a more complex compositional procedure characterized by the systematic imitation of a principal theme, known as the subject, within simultaneously sounding melodic lines (counterpoint).3

Historically, the canon is considered the earlier, more restrictive technique, while the fugue represents a later stage in the evolution of imitative counterpoint. While canonic pieces were sometimes labeled fuga as early as the 14th century, the fully developed fugue emerged from the imitative beginnings of late 16th-century canzonas and ricercares. Unlike the strict, continuous repetition found in a canon, a fugue allows for greater variety and development of its subject through techniques such as stretto, inversion, and the use of countersubjects.14