*A window with no glass* >! A lens is like a window but the lens of an eye has no glass. *A student with no class* >! Another word for student is pupil but the pupil of an eye has no class. *A sea in any season* >! "A sea" sounds like "I see", which the eye does year round. *An epistle? No, a threesome* >! Another word for epistle is letter. An eye is three letters. The title: *An easy positive riddle* >! "Easy" sounds like "I see". Eye sounds like “aye”, a positive answer, the sí of the sea.