basics: scales
The two main scales in 18th- and 19th-century tonal music are the major and minor scales:
Because the minor scale does not contain a leading note, it can be added by raising the 7th note, or the 6th and 7th notes:
EXPLORING KEYS & SCALES
Since preluding is a discipline that involves training in all keys, a general introduction to all 24 keys is recommended. The circle of fifths provides a good framework, like in the following example taken from The Material used in Musical Composition (1889) by Percy Goetchius:
The following exercise is very practical and can be learned easely at the keyboard.
The following document gives an overview af all the major and minor scales including fingerings:
For more information about scales, check 19th-century piano methods in the 'publications' section.