Grief is the opposite of Joy. Joy is the opposite of Pain. 
Feed is related to Past. Past is a different concept from Future. Future is related to Back. Back is a type of Strengthen. 
Grief <--Antonym--> Joy <--Antonym--> Pain 
Feed <--RelatedTo--> Past <--DistinctFrom--> Future <--RelatedTo--> Back --IsA--> Strengthen 