[BLANK_AUDIO]In lecture two, Zack and I described theconcept of keys and key signatures.You'll remember that when we travelthrough the octave usingscales, we get distinctive internalpatterns of intervals that arise.And you'll remember the major scale hasthat distinctivepattern of tone, tone, semitone, tone,tone, tone, semitone.>> And you remember us talking about keysignatures andsaying that they're a way for us to signalrightin the very start of a piece of music,whatsharps and what flats we're going to havein any given key.This came from the idea that some scaleswere built up, and we needed touse some sharps and some flats when wewere using a tonic that wasn't C.So, this then allows us to use any one ofour pitchclasses, and that is any one of the 12note names asour tonic, so that we can build patternsof tones and semitonesor scales, or melodies or chords in any ofthese given keys.Now, it'll help you, when you're trying tobecome fluent in readingand writing music, to try and get thesememorized as much as possible.If you look back at week two, there aresome tipsand mnemonic devices for how to actuallygo about doing this.>> Okay so, at the start of this lecture,we were lookingat triads, and we were looking atperceptual effect of those note groupings.So that one, just one of the notes thatwas there, was the more important one, wasthe one we can use to identify that triad,had that overarching label for that triad.Well, within a key, the relationshipsbetween andwithin those triads and how we use themcanalso contribute to that overarching senseof tonality,by which we mean the quality of the key.>> So we've been using words like harmony andharmonic structure.And these are words and phrases that youhear when we're talking about music often.What do I actually mean by these phrases?Now is a probably a good time to actually

think a wee bit more precisely about we'resaying.>> Yeah.Well, harmony describes the effect ofthose triads that we've been talkingabout.And the relationships and the patternsbetween thetriads when we use them in a key.Key and harmonic structure, or key andharmony, are the twomost important building blocks for musicthat sits in a tonal tradition.So to explain this more, I'm now going tosing you a familiartune; you can follow the melody on thestave notation on the screen.Instead of using the words that you'll befamiliar with, I'mjust going to use the scale degree numberswhen I'm singing.[MUSIC]One, one, five, five, six, six, five.Four, four, three, three, two, two, one.Five, five, four, four, three, three, two.Five, five, four, four, three, three, two.One, one, five, five, six, six five.Four, four, three, three, two, two, one.[MUSIC]You can hear a couple of things, a coupleof features in that familiar song.The first one that we're going to pointout,is that you got a very strong tonalidentity.[MUSIC]I was singing in C.[MUSIC]And C is the tonic.And it came across very clearly.>> Another thing we can think aboutrelates to the structure of the music.So as the melody progresses, there arepoints.It comes to rest, but it doesn't feelcompletely finished.There are other points where the musiccomes torest but does feel finished and does feel'closed'.Now these points are what we know ascadences.>> Let's look at a couple of thosecadences from the familiar song.A cadence that comes to rest but soundsopen and unfinished.We've got one up above the world so high,like a diamond in the sky.[MUSIC]It rests, but it's not finished.

And we can compare that with the return atthe end.Twinkle, twinkle little star, how I wonderwhat you are.[MUSIC]What's causing that effect then?>> Well, in order to think about, wereally want to look at the scale degreesagain.Before we do that, let's just think aboutthe key of C as a whole.So we got, one, two, three, four, five,six,seven, and back to one again for ourtonic.>> We know that triads that are built onthe tonic.[MUSIC]And the dominant.[MUSIC]Have particularly strong structuralproperties, harmonically, they're verystrong.So let's see which scale degrees featurein the dominant triad.[MUSIC]We've got a five.[MUSIC]And we've got a seven.[MUSIC]And we've got a two.[MUSIC]I mean, we've got the fifth and theseventh and the second degrees of thescale present.For the tonic triad, we've got the first,andthe third, and the fifth degrees of thescale present.>> So let's go back to our melody againand look at this in a bit more detail.Well, if we look at one of the points thatthe music came to rest but didn't feelfinished, we get.>> We had five, five, four, four, three,three, two, five, five, four, four, three,three, two.>> So the five and the two really standout to us, and that's what gives usthat feeling - of it not feeling quitefinished,the two notes that belong to the dominantchord.>> Especially when we compare that to thephrase that did sound finished.Four, four, three, three, two, two, one.>> And when we're coming down there, we'recoming back away from the tonic chord.Sorry... we're coming back from the DOMINANTchord back to the the tonic chord.

And this is another example of a cadence.>> So music theory, we call those cadenceswhere wesit and hang around but at the dominantopen, unfinished chord.We call that an imperfect cadence.We contrast that with a perfect cadence.And that's where we've traveled back froma dominant.[MUSIC]Chord back to the tonic.[MUSIC]And we've come home again.There's a lot more to say about cadences.And we'll go a bit further in this lecturelateron, but you'll go further still in thefinal lecture.[BLANK_AUDIO]