Six Doors
   One may wonder what the term 'door' means. A door is the means
through which citta experiences an object. Seeing experiences visible
object  through the eye-door. The eye-door is the eyesense, a
phenomenon (rupa), which is capable of receiving visible object. Eyesense
itself does not see but it is a condition for seeing. There are six doors of
eyes, ears, nose, tongue, bodysense and mind- door. There is no self who
experiences objects. There are only different types of cittas, succeeding
one another, which experience an object through one of the six doors.

Topic 16