فالأول منهما يوجب صحة الاستعارة من الطرفين
The first pattern permits figurative transfer in both directions.
Where a legal cause is directly related to its effect, the language of the cause can point to the effect, and the language of the effect can point back to the cause. This is not an assertion that the two words are synonyms. Their legal relationship provides the ground for transfer.
Purchase (shirāʾ) denotes acquiring by buying; ownership (milk) denotes the resulting legal entitlement. Purchase is a recognized means of obtaining ownership, making this pair a useful test case.