What is an augmented interval?

An augmented interval is defined as when a perfect interval is raised by a half step. This means that you start with a perfect interval—such as a perfect fifth or perfect fourth—and then increase its size by a half step, effectively making it "augment" the distance between the two notes.

In musical terms, this alteration results in a unique sound that often conveys tension or a sense of movement. For instance, if you take a perfect fifth (which consists of seven half steps) and raise it by a half step, it becomes an augmented fifth (which consists of eight half steps). This concept is fundamental in music theory as it helps deepen the understanding of how intervals function and contribute to harmony and melody within music composition.

The other definitions provided in the options do not align with the standard music theory definitions of intervals, thus reinforcing the correctness of the identification of an augmented interval as raising a perfect interval by a half step.