Two.
57. What are they?
Regular and irregular.
58. What is a Regular derivative?
One that is formed by the addition of affixes without changing the letters in the primitive part (except final e silent).
59. What is an Irregular derivative?
One in which the letters of the primitive part are changed.
60. In using Affixes, what rule should be observed?
The affix and root should be from the same language.
61. Is the same rule to be observed in forming Compound words?