Key Signatures

Look at the very start of a staff, just after the clef. Sometimes you will see a little cluster of sharp or flat signs sitting there before any notes begin. That cluster is the key signature, and it sets the rules for the whole piece.

A key signature says "these notes are always sharp" or "these notes are always flat," from here to the end, unless the music says otherwise. It saves the composer from drawing a sharp or flat next to every single one of those notes.

Find a piece with one or two sharps right after the clef. Those sharps are the key signature, telling you which notes to raise all the way through.

A key signature is a piece of notational economy. A tonal piece centers on one home key, and that key's scale raises or lowers the same handful of notes every time they occur, so notation states those alterations once at the front rather than marking every instance. What could be dozens of accidentals per line collapses into a few symbols after the clef.

Because each major and minor key is a specific scale, and each scale sharpens or flattens a specific set of notes, the exact sharps or flats a piece carries narrow its key to one major key or its relative minor. Reading the signature tells you what scale a passage is drawn from before you analyze a note.

Sharps do not show up in a key signature in just any order. They always appear in the same fixed sequence: F, C, G, D, A, E, B. A key with one sharp has F-sharp. A key with two has F-sharp and C-sharp. Three adds G-sharp, and so on down the list.

To remember it, use a classic phrase: "Father Charles Goes Down And Ends Battle." The first letters spell F C G D A E B.

Say the sharp order out loud a few times, then write the first three: F-sharp, C-sharp, G-sharp. That is the start of the line every sharp key follows.

The sharp order F C G D A E B is a chain of ascending fifths, and that structure is why sharps accumulate so regularly. Each step up a fifth to a new key requires raising exactly one more note to preserve the major pattern, and that note is always the next one along the chain. The sequence is a consequence of how scales a fifth apart differ by a single pitch.

There is a neat internal rhythm to it as well. The order of sharps and the order of flats are mirror images, one read forward and the other backward, because sharpening by fifths and flattening by fifths run in opposite directions around the same twelve notes. Knowing one order effectively gives you the other reversed, which halves what there is to memorize.

Flats have their own fixed order, and it is the sharp order flipped backward: B, E, A, D, G, C, F. A key with one flat has B-flat. Two flats are B-flat and E-flat. Three add A-flat, and on it goes.

The first four letters spell a real word, BEAD, which makes them easy, and then it finishes G, C, F.

Write the first three flats in order: B-flat, E-flat, A-flat. Every flat key signature starts with B-flat and adds flats in this order.

The flat order, B E A D G C F, runs by descending fifths, the exact reverse of the sharp order's ascending fifths, which is why the two sequences are mirror images. Moving down a fifth to a new key lowers one additional note each time, and that note is the next flat along the chain, so flats accumulate as regularly as sharps do, just in the opposite direction.

This mirroring reflects a symmetry in the whole key system. The sharp keys and flat keys spread out in two directions from C, which has neither, and the further you travel either way the more alterations you carry, one per step. The two orders are the same journey around the notes taken clockwise or counterclockwise, an idea the Circle of Fifths makes visible in the next class.

Here is a trick to name a sharp key just by looking. Find the last sharp on the right, then go up one half step (the very next key up). That note is the name of the major key. Two sharps end on C-sharp; a half step up is D, so two sharps means D major.

Flats have their own trick. For two or more flats, look at the second-to-last flat, and that flat is the name of the key. Four flats end with D-flat as the last, and A-flat as the second-to-last, so four flats means A-flat major. The exceptions to just remember: no sharps or flats is C major, and one flat is F major.

Practice on a signature with three sharps. The last sharp is G-sharp; up a half step is A. Three sharps is A major.

The naming shortcuts work because of where the altered notes sit in the scale. The last sharp added is always the seventh degree, the leading tone, of the key it defines, so it stands just below the tonic and points up to it. It is a direct read of the scale: raising the fourth degree of the old key, which becomes the seventh of the new key, is what turns one key into the next one up.

The flat rule has the same kind of basis. As flats accumulate, the most recently added flat is the fourth degree of its key, and the flat added just before it lands on the tonic, which is why the second-to-last flat names the key. Both shortcuts are just efficient ways of reading which scale a given set of alterations produces, so understanding the scale makes the tricks memorable rather than mysterious.

A key signature and a scale are two sides of the same thing. The sharps or flats in the signature are exactly the notes that the piece's scale raises or lowers. If a piece is in G major, its scale has an F-sharp, so its key signature has one sharp, F-sharp. The signature is just the scale's changes, written once at the front.

There is one more twist. Each key signature actually fits two keys, a major one and its relative minor, because they share the same notes. One sharp is G major, and it is also E minor, its relative minor. You tell which by listening for which note sounds like home.

Play a piece with one sharp and notice whether it feels like it rests on G or on E. Same signature, two possible homes.

A key signature encodes a scale, and reading it fluently means seeing the scale behind the symbols rather than the symbols alone. Because each key is a fixed pattern of steps requiring specific alterations, the signature and the scale are two representations of one object, and moving freely between them is much of what key literacy amounts to.

The relative-key pairing is where the signature stops being a label and becomes a tool. Sharing a signature, a major key and its relative minor draw on nearly the same notes and chords, so composers slip between them without changing the key signature, usually adding only the raised seventh of the minor key, and analysts must read context, not just the front of the staff, to say which is in force. The signature fixes the note collection, and the music decides which note is heard as the center.