Thelonious
A pocket guide to music theory
Only for iPhone
Free · Designed for iPhone. Not verified for macOS.
iPhone
Learn Music Theory & Master Every Key
Thelonious is a music theory app designed to help you understand keys, chords, scales, and harmony through clear, visual layouts.
Explore major keys, review scale notes, and study diatonic chords in a format built for both learning and quick reference. Thelonious connects theory to real playing with chord progressions, guitar mode charts, and CAGED system material.
Use Thelonious to:
• Explore major keys and their scale notes
• Understand diatonic chords and key relationships
• Learn relative minor and dominant chords
• Study chord progressions and harmonic movement
• View guitar modes and CAGED chord charts
Whether you’re learning the fundamentals or deepening your understanding of harmony, Thelonious makes music theory easier to read, understand, and apply.
Ratings & Reviews
The developer, Robert Natale, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .
Data Not Collected
The developer does not collect any data from this app.
Accessibility
The developer has not yet indicated which accessibility features this app supports. Learn More
Information
- Seller
- Robert Natale
- Size
- 36.1 MB
- Category
- Music
- Compatibility
Requires iOS 15.1 or later.
- iPhone
Requires iOS 15.1 or later. - iPod touch
Requires iOS 15.1 or later. - Mac
Requires macOS 12.0 or later and a Mac with Apple M1 chip or later. - Apple Vision
Requires visionOS 1.0 or later.
- iPhone
- Languages
- English
- Age Rating
4+
- 4+
- Copyright
- © 2026 Rob Natale