"Canon in fugue at the interval of a fourth" describes a sophisticated musical composition that combines two distinct contrapuntal techniques: canon and fugue, with a specific characteristic in the canonic imitation. Let's break it down:
1. Canon:
- At its core, a canon is a musical form where one or more voices (or instrumental lines) imitate the melody of a leading voice.
- Think of it like a round (like "Row, Row, Row Your Boat"), but potentially more complex.
- The following voice(s) enter after a specific delay and often at a different pitch than the original melody.
2. Fugue:
- A fugue is a contrapuntal compositional technique for a set number of voices (typically 2 to 5).
- It's built on a central subject (a short melody or theme) that is introduced at the beginning by one voice alone.
- Subsequent voices enter in imitation of the subject, often at different pitch levels (typically a fifth above or a fourth below the original). This initial section is called the exposition.
- After the exposition, the subject is developed and appears in various keys and voices throughout the piece, often interwoven with episodes (sections that don't feature the complete subject).
- Fugues emphasize the independent melodic lines of each voice and their intricate interplay.
3. "At the interval of a fourth":
- This specifically describes the relationship in pitch between the original melody in the canon and its imitation.
- A fourth is a musical interval spanning four diatonic steps (including the starting and ending notes). For example, from C up to F is a perfect fourth.
- Therefore, when a new voice enters in the canon, it will be singing or playing the same melody as the first voice, but starting either four steps higher or four steps lower in the musical scale.
Putting it all together:
A "Canon in fugue at the interval of a fourth" is a composition that:
- Has a canonic structure: One voice imitates another after a delay.
- The imitation occurs at the interval of a perfect fourth: The following voice starts its version of the melody four diatonic steps away from the original.
- Is also structured as a fugue: The canonic melody (or a significant part of it) serves as the subject of the fugue. This subject is then introduced by each voice in turn (the exposition), and subsequently developed through various contrapuntal techniques characteristic of a fugue, such as inversions, stretto (overlapping entries of the subject), and episodes.
In essence, it's a piece where the principle of canonic imitation at a specific interval is integrated into the broader, more complex framework of a fugue. This creates a very intricate and intellectually engaging musical texture where the listener can follow the same melody appearing in different voices, offset in time and pitch, while also experiencing the development and interplay of these melodic lines within the fugal structure.
Think of it as a double layer of contrapuntal ingenuity, where the strict imitation of the canon is woven into the more flexible and developmental nature of the fugue. It demands significant compositional skill to execute effectively.