Augmented third

The augmented third (A3) is an enharmonic interval spanning 5 semitones. It sounds like a perfect fourth, but its spelling marks an expanded third with distinct harmonic identity.

Construction and spelling

A3 is written as a third raised by one semitone, such as C to E# or A to C##. Even when the sound equals P4, the letter pattern preserves third-based function. This distinction is critical in advanced chromatic and theoretical notation.

Harmonic and melodic usage

In practice, A3 appears mostly in notation where interval function and voice-leading spelling matter more than acoustical equivalence. It can clarify altered chord tones and directional transformations. Its significance is largely structural and analytical.

Examples

• Enharmonic spellings in highly chromatic harmony
• Analytical contrast between sounding P4 and written A3
• Advanced voice-leading and interval naming exercises

In practice

Practice A3 by writing and naming intervals, then compare C-E# with C-F to hear same distance but different theoretical labels. Combine notation drills with ear comparison. Strong A3 fluency improves precision in harmonic analysis and composition spelling.