Music Theory

This hub collects StrumAndKey's 25 music theory topics, deliberately ordered from foundational to advanced rather than alphabetically, because most of these topics genuinely build on each other. How Chords Are Built and Major Scale Formula sit at the base — the stacked-3rds logic behind every triad, and the whole/half-step pattern behind every major scale, are the two ideas nearly every other theory page here assumes the reader already has.

From there, the topics split into a few real clusters rather than one linear sequence. Intervals Explained, Key Signatures Explained, and The Circle of Fifths Explained form a "how pitches and keys relate to each other" cluster — understanding semitone counting is what makes key signatures make sense as a direct consequence of the major scale formula rather than a memorization exercise, and the circle of fifths is best understood as that same key-signature logic laid out visually rather than a separate topic to memorize from scratch.

Diatonic Chords, Chord Progressions, Chord Function, Secondary Dominants, and Chord Substitution form a harmony-in-motion cluster: why every key naturally produces exactly seven triads, how those seven triads take on real functional roles (tonic, subdominant, dominant), which progressions recur constantly across genres and why they work, and the two real techniques (borrowing a foreign V chord, or swapping a chord for a harmonically-related one) that let songwriters and arrangers step outside plain diatonic harmony deliberately rather than by accident.

Chord Inversions, Chord Extensions, Add Chords vs. Extended Chords, Suspended Chords Explained, and Power Chords Explained form a "what a chord voicing can actually do" cluster — moving a chord's bass note, stacking tensions past the 7th, and the specific ways suspended and power chords deliberately remove or alter the 3rd that would otherwise define a chord's quality.

A genuinely instrument-specific cluster covers what's physically different about each of StrumAndKey's three instruments: Guitar Tuning Explained (why standard EADGBE isn't a single repeating interval), Barre Chords Explained (the mechanics of one-finger multi-string technique), Piano Fingering Basics for Chords (the real 1-2-3-4-5 conventions), and Ukulele Reentrant Tuning Explained (why a ukulele's high G string makes it genuinely not "a small guitar"). Open vs. Closed Chord Voicings and How to Read a Chord Diagram sit alongside these as cross-instrument practical topics.

Modes Explained is the deepest theory topic in the roster — the seven modes of the major scale as genuinely distinct sounds rather than "the same notes starting somewhere else," which only really clicks once natural minor (itself a mode, Aeolian) is already understood from the scales hub. The Nashville Number System and How to Transpose Music round out the practical-application end, covering how professional session musicians and working arrangers actually move progressions between keys without rewriting everything from scratch. Rhythm & Strumming Patterns is StrumAndKey's one topic that's primarily about time rather than pitch — how down/up-strum notation and common time-signature patterns interact with the chord vocabulary covered everywhere else on the site.

A genuinely common question this hub exists to answer honestly is "do I need to learn all of this before I can play songs?" — and the honest answer, reflected in how these 25 pages are written, is no. A guitarist can memorize five open chord shapes and strum along to hundreds of songs with zero formal theory knowledge; theory becomes useful once a player wants to understand WHY certain chord combinations sound good together, transpose a song to a more comfortable key, write original progressions instead of copying existing ones, or communicate with other musicians using a shared vocabulary instead of trial and error. StrumAndKey's theory pages are written for that second stage — the player who already has some chords under their fingers and wants the "why" behind them — rather than as a prerequisite gate before touching an instrument at all.

Several topics in this hub exist specifically to resolve confusions StrumAndKey's own chord and scale pages generate once a reader starts comparing entries across the site: Add Chords vs. Extended Chords exists because add9 and 9th chords look deceptively similar in name; Chord Extensions exists because a theoretically "complete" 13th chord almost never matches what real fingering diagrams show; and How to Read a Chord Diagram exists because the same visual symbols (open circles, X marks, barre lines, finger numbers) recur on every single chord page on the site and are worth explaining once, properly, rather than assuming they're self-evident.

Several topics deliberately cross instrument boundaries rather than treating guitar, piano, and ukulele as three separate silos, because the underlying music theory genuinely is the same across all three — a major triad is root-3rd-5th whether it's fingered on a fretboard, played on a keyboard, or strummed on four reentrant-tuned strings. What differs, and what the instrument-specific topics in this hub (Guitar Tuning Explained, Barre Chords Explained, Piano Fingering Basics for Chords, Ukulele Reentrant Tuning Explained) exist to explain honestly, is how each instrument's physical layout constrains or shapes which voicings of that same theoretical chord are actually playable.

Rhythm & Strumming Patterns is worth calling out as the one topic in this hub that isn't really about harmony at all — chord choice and rhythm are two genuinely separate dimensions of a piece of music, and a player can know every chord on this site perfectly and still sound unconvincing if the strumming or comping rhythm underneath doesn't fit the song's actual feel. This topic exists specifically because that gap (theory knowledge without rhythmic vocabulary) is a real, common plateau many self-taught players hit.

Nashville Number System deserves a specific practical note: it's not a theory topic in the abstract sense the way intervals or key signatures are — it's a real, working notation system used by professional session musicians (originating in and named for Nashville's country and gospel recording studios) so a band can rehearse or record a song in whatever key best suits a singer that day without anyone needing to rewrite chord charts from scratch. Understanding it is directly useful for anyone who plays with other musicians regularly, not just an academic curiosity.

This hub's ordering reflects a genuine teaching philosophy worth stating outright: theory is presented here as a tool for understanding what a player's hands and ears are already doing, not as a gatekeeping prerequisite that has to be mastered before touching a chord page. A complete beginner is entirely welcome to skip straight to a chord or scale page, learn a shape, and come back to these 25 topics only once curiosity or a specific confusion (why does this chord sound like that one? why does this progression feel resolved?) sends them looking for the "why."

Every topic page in this hub is written as a standalone explanation with its own real FAQ, but the genuine dependencies between topics are called out in-body wherever one idea builds directly on another, and every page links back to the specific chord and scale pages that put the theory into practice. Cross-referencing between this hub and StrumAndKey's chord and scale pages runs in both directions and is deliberate rather than incidental — a theory page explaining why a ii-V-I progression works links out to the actual m7, dominant 7, and maj7 chord pages a reader would use to play one, and a chord page explaining a specific voicing links back to whichever theory topic explains the underlying logic, which is what keeps this hub from reading as an abstract textbook detached from the rest of the site's real, playable content.

Reading these 25 pages start to finish is a genuinely reasonable way to build a working foundation in music theory in a weekend, but it's just as reasonable to treat this hub as a reference shelf, dipping in only when a specific question comes up while working through a chord or scale page elsewhere on the site — both approaches are supported equally, and neither is treated as the "correct" way to use this hub — the 25 topics are written to stand alone as thoroughly as they work in sequence, so a reader arriving from a search engine at any single page gets a complete, self-contained explanation rather than one that assumes prior pages in the hub have already been read — genuine dependencies are always named explicitly in-body, with a direct link to the prerequisite topic, rather than silently assumed, so no reader is ever left guessing what background knowledge they're supposedly missing before a given explanation can actually make full sense to them.

Formal music education (a conservatory, a university theory sequence, a long-term private-lesson program) covers all 25 of these topics and considerably more, typically over years rather than in one sitting — StrumAndKey's theory hub is not a substitute for that depth, but a genuinely useful, honestly-scoped reference for the specific, foundational-through-intermediate concepts that directly explain the chord and scale vocabulary documented across the rest of the site, written so a self-taught or casually curious player can look up exactly the piece they need without wading through an entire textbook to find it.