chord 之後有個數字, 個數字代表乜 ?

果D數字代表住數字低音, 亦即係Figured Bass
而Figured Bass係咩呢其實就只係代表住....

Root Position：6/5

First Invertion : 4/3

Second Invertion : 4/2

用C Major既 IV 同埋 V 舉個例

C Major → IV 6/5
即係C Major第4個Chord既Root Postion
F A C

C Major → IV 4/3
即係C Major第4個Chord既First Invertion
A C F

C Major → IV 4/2
即係C Major第4個Chord既Second Invertion
C F A

C Major → V 6/5
即係C Major第5個Chord既Root Postion
G B D

C Major → V 4/3
即係C Major第5個Chord既First Invertion
B D G

C Major → V 4/2
即係C Major第5個Chord既Second Invertion
D G B

C Major → V 7
即係C Major第5個Chord既Root Postion再加個Key既第7音
禁當然V 7另外都仲可以分Root Postion, First Invertion同埋Second Invertion
而佢既Root Postion就係F A C E

希望你明我講咩啦^^

C Major → V 7
C Major既5,7chord, 唔係G B D F# ?

Figured bass was very popular during the Baroque period, and was specially written for the harpsichord players, whose jobs were to play the basso. They were trained and could play it out immediately after reading the scores, which modern players can never achieve.

Proceeding to the Classical period, it became outdated and very few composers made use of it, one of those was Mozart. At that time, he used figured bass to teach his students.

Well, back to your question.

no figuring = 5/3 (root position of triad)
6 = 6/3 (first inversion of triad)
6/4 = 6/4 (second inversion of triad)

7 = 7/5/3 (root position of seventh chord)
6/5 = 6/5/3 (first inversion of seventh chord)
4/3 = 6/4/3 (second inversion of seventh chord)
4/2 = 6/4/2 (third inversion of seventh chord)

Figured bass is somehow a numeral indication of the variations of a chord, take 4/3 as an instance, old musicians shortened 6/4/3 as 4/3 for better sight.
If the root of the bass line is an A, then by counting intervals 3, 4 and 6, we get C, D and F. To form a chord, it must be D/F/A/C, that is, if it is in G major, the chord will be a dominant seventh in second inversion, V4/3. However, there may not be having all chordal tones appearing, F can be omitted in this case, as the root and seventh are most important for a seventh chord.
One more example, if you find an A on the bass line but with a 6 below, it probably has a F on the melody line. Why is that? Simply because it is the first inversion of a triad, F/A/C.

Apart from numbers, there are also marks such as accidentals, a +, a `. Send a letter to me if your want further details.

By the way, I actually don't reckon what you met was a figured bass, because figured bass is not like the Roman numeral system, it never show its harmonic function, it contains numbers and marks only, showing of the Roman numbers should be a kind of harmonic progression.

figured bass 即係數字低音. 佢寫係個chord上面. 令到你好容易見到個chord 就知係 root prosition or first inversion 等等.

The number is FIGURED BASS. For example, II 6, mean the supertonic chord in first inversion.

Benjamin