Solve is a type of Understand. Solve entails/necessarily involves Reason. Reason is a synonym of Ground. you are likely to find Dirty in/at/on Ground. 
Field is a synonym of Plain. Plain is a synonym of Normal. 
Understand <--IsA-- Solve --Entails--> Reason <--Synonym--> Ground <--AtLocation-- Dirty 
Field <--Synonym--> Plain <--Synonym--> Normal 