Drift is a type of Change. Clear is a type of Change. 
Vary is etymologically related to Various. Vary is a type of Village. you are likely to find Cow in/at/on Village. Cow is related to Sheep. 
Drift --IsA--> Change <--IsA-- Clear 
Various <--EtymologicallyRelatedTo-- Vary --IsA--> Village <--AtLocation-- Cow <--RelatedTo--> Sheep 