How is the primary denominator (Asl al-Mas'alah) determined when multiple shares are present?
Chapter on the Roots of Inheritance Shares that Increase (Awl)
Al-Mughni
Book of Inheritance Shares (Farā'id)
Primary text
If a case contains only one fixed share, its denominator is taken directly from its own requisite denominator. If two shares are present and one denominator is a factor of the other, the larger denominator is taken as the primary denominator. If two shares are present and neither denominator is a factor of the other, the primary denominator is found by multiplying one denominator by the other, or by finding their least common multiple (Wafq). The principle of Awl (increase in shares) arises when the total shares exceed the total estate, which occurs in cases where shares crowd each other and the estate cannot accommodate them.
Supporting text
When a case involves one-half and any share from the second type (one-third or two-thirds), the primary denominator is 6, calculated by multiplying the denominator of one-half (2) by the denominator of one-third/two-thirds (3).