Partial is related to Unfair. Unfair is the opposite of Justice. Justice is related to Truth. Truth is the opposite of False. 
Validity is a type of Situation. Challenge is a type of Situation. 
Partial <--RelatedTo--> Unfair <--Antonym--> Justice <--RelatedTo--> Truth <--Antonym--> False 
Validity --IsA--> Situation <--IsA-- Challenge 