How do vertically stacked notes show chords in Western staff notation?

In Western staff notation, notes are stacked vertically on the staff to represent chords, indicating that the different tones are to be sounded simultaneously.12

This vertical alignment serves as a visual framework that allows musicians to quickly identify the harmonic intervals—the pitch relationships between simultaneous tones—and the overall harmonic structure of the music. By placing note heads on different lines or spaces of the same staff at the same horizontal position, the notation clearly displays the combination of pitches that form a chord. This system is essential for notating complex textures, such as polyphony, where multiple independent melodic lines or harmonic structures interact at once.13