The Four Paramattha Dhammas - Conditioned Dhammas

Citta, cetasika and rūpa only arise when there are the right conditions, they are conditioned dhammas (in Pāli: sankhāra dhamma). Seeing cannot arise when there is no eyesense and when there is no visible object; these are necessary conditions for its arising. Sound can only arise when there are the right conditions for its arising. When it has arisen it falls away again. Everything which arises because of conditions has to fall away again when the conditions have ceased. One may think that sound stays, but what we take for a long, lasting moment of sound are actually many different  rūpas succeeding one another.

Topic 174