Spend is a type of Pay. Pay is related to Spending. Spending is related to Debt. Debt is related to Obligation. 
Phenomenon is related to Cause. Cause is related to Conservation. 
Spend --IsA--> Pay <--RelatedTo--> Spending <--RelatedTo--> Debt <--RelatedTo--> Obligation 
Phenomenon <--RelatedTo--> Cause <--RelatedTo--> Conservation 