ಅರ್ಥ : Morally or legally constraining or binding.
							ಉದಾಹರಣೆ : 
							Attendance is obligatory.
							An obligatory contribution.
							
Possible but not necessary. Left to personal choice.
optionalಅರ್ಥ : Required by obligation or compulsion or convention.
							ಉದಾಹರಣೆ : 
							He made all the obligatory apologies.