Scale Degrees & Identifying the Key

Which scale degree is the supertonic, and where does its name come from?

Why is the mediant (3rd degree) such an important note when classifying a scale?

Two scales share the same tonic and dominant but differ in quality (major vs minor). Which degree tells them apart, and why?

Why is the leading tone described as "essential" for identifying a piece's key, especially in minor?

A key signature alone never points to exactly one key. How many keys does it give you, and which two?

Given the two candidate keys from a key signature, what is the simplest melodic clue that usually reveals the tonic?

Both candidate keys share a signature. What accidental, if present, proves the piece is in the minor key rather than the major?

A piece has one sharp in the key signature, contains no accidentals, and ends on G. Major or minor, and which key?

A one-sharp piece contains a D# and ends on E. Why is it E minor and not G major?

Why is assuming "the major key" the safe default whenever you see a key signature a mistake?

Identify the key of this short melody.

Why does each scale degree get a name (tonic, dominant, mediant, etc.) instead of just being called "note 1, note 2…"?

What is the name and Roman numeral of the 1st degree of a scale, and what makes it special?

Which scale degree is the mediant, and why is it called that?

Don't confuse them: which degree is the mediant and which is the submediant?

Which scale degree is the subdominant, and where does it sit relative to the dominant?

Which scale degree is the dominant, and why is it considered so powerful?

The 7th degree can be called two different names. What are they, and what single fact decides which one applies?

A scale's 7th degree sits a whole tone below the tonic above it. Is it correct to call it the leading tone?