I was wondering what the Roman Numerals are. I though it was I,III, V, for major key but that was not it.
People usually use
- capital letters for major chords, like I,IV and V
- lower case for minor chords like ii,iii,vi
- lower case with diminished symbol for diminished chords, like viiø (for half diminished ones) and vii° for diminished ones.
But, I have seen people symbolizing the minor chords with capital letters as well.
The Roman Numerals that indicate major, minor, and diminished are the same in any kind of key and all keys will have seven possible Roman Numerals from 1 to 7 one for each scale degree. The specifics for the quality of the chords are as follows:
- A major chord will always be represented by an upper case Roman Numeral I.E. : I, II, III, IV, V, VI, VII are all major.
- A minor chord will always be represented by an lower case Roman Numeral I.E. : i, ii, iii, iv, v, vi, vii are all minor.
- A diminished chord will always be represented by an lower case Roman Numeral and a circle. I.E. : i°, ii°, iii°, iv°, v°, vi°, vii° are all diminished.
- An augmented chord will always be represented by an upper case Roman Numeral I.E. : I+, II+, III+, IV+, V+, VI+, VII+ are all augmented.
So let's look at the key of C major and the chords natrually built from it. Because we naturally get the chord C, Dm, Em, F, G, Am, and Bdim, we end up with the Roman Numerals I, ii, iii, IV, V, vi, and vii°.
For more information about this, you can view the lessons about Roman Numerals on musictheoy.net which go a little more in depth on this topic, but covers the same points.
Shevliaskovic already explained the roman numerals in a key, but let me explain the "1-3-5" you mentioned in your post, because this is a different concept.
1-3-5 are the note intervals used to create a major chord from the major scale.
For example, take the C major scale:
If you take the notes labeled 1-3-5 from the C major scale you get C-E-G, which is a C major chord.
This process is also called "stacking 3rds" because the notes are a 3rd apart. You can apply this process to each note in the major scale to build different the chords from the scale.
Move to the next number and take the notes labeled 2-4-6 you get D-F-A which is a D minor chord.
If you continue this process for all the notes, you get:
1-3-5 = C-E-G = C major chord 2-4-6 = D-F-A = D minor chord 3-5-7 = E-G-B = E minor chord 4-6-1 = F-A-C = F major chord (note the wrap around back to "1" here) 5-7-2 = G-B-D = G major chord 6-1-3 = A-C-E = A minor chord 7-2-4 = B-D-F = B diminished chord
Now, if you look at the pattern of chords created here, you get:
C major D minor E minor F major G major A minor B diminished
Notice the order of the major, minor, and diminished chords.
Maj min min Maj Maj min dim
Now apply the roman numeral convention that Shevliaskovic mentioned to this pattern and you get:
I ii iii IV V vi vii°
We've come full circle right back to the roman numeral pattern. :) So while the "1-3-5" note intervals and the "I IV V" roman numerals are different concepts they are also closely related.
Major keys use the one major (I) the four major (IV) and the five major (V). When forming chords (triads) using the notes available in a diatonic major key (7 possible notes) the one, four and five chords end up being major, the two, three, and six chords minor and the seventh diminished.
It is common to use an "uppercase" Roman Numeral to represent major chords (I, IV, V) and lower case to indicate minor (ii, iii, vi) and the little ° for diminished (vii°). But I have seen it represented differently so that is not a hard and fast rule about how to denote major versus minor. It is a hard and fast rule that the I, IV and V chords in any diatonic major key will be major and the only major chords that can be formed from the notes in that key.
Here is a chart showing the chords for all the major keys. The T and S at the top of this chart are for Tone (T) and Semitone (S) and shows that in a major key the intervals between notes in a diatonic major scale are - tone, tone, semitone, tone, tone, tone semitone. Also referred to as whole, whole, half, etc. (steps).