Compared with the British empiricism of the 17 th and 18 th centuries,empiricism in the context of the philosophy of science values the epistemological difference between the unobservable and the observable.Bas van Fraassen,the founder of constructive empiricism,chooses the objectual notion of observation toavoid the challenge of the thesis of theory-ladenness.And he insists that observation is unaided human perception,and completely denies the cognitive value of scientific instruments.The role that the thesis of theory-ladennes plays in the debate between scientific realists and constructive empiricists about the unobservable-observable distinction(UOD)is rather subtle.Unfortunately,Van Fraassen′s notion of observation is unconvincing due to his neglecting the intentional character of scientific observation.