In Zeami’s treatises, one of the criteria of a well written Noh play is “a reliable source”（“honzetsu tadashi”）. This is repeated several times, for instance in the third （Daisan mondōjōjō） and sixth part （Kaden dairokkashū） of Fūshikaden, in Sandō （1423） or Kakyō （1424）.“ A reliable source” is a widely acknowledged classic literary work, which is to be used as a source material for creating a Noh play.In Kaden dairokkashu Zeami refers to“ ōyōnaru Nō” as being Noh created based on an especially reliable source. As it is a Noh of high rank, the actor’s performance should display few highlights. On the other hand, “chiisaki Nō” may not have a great source, but still has to be elegant, although its performance is detailed, with highlights of movement and gestures.I would like to draw attention to the fact that here“ ōyōnaru Nō” and“ chiisaki Nō ” are referred to in comparative terms. There is a difference of rank between“ ōyōnaru Nō” and“ chiisaki Nō”, and that rank differs depending on the quality of the source material for a Noh play. Moreover, in contrast to “ōyōnaru Nō”, which is to be performed with a certain restraint of movement and gestures“, chiisaki Nō” requires meticulous acting. In other words, in Zeami’s view, the density of acting gestures employed during the performance differs depending on the rank of a Noh play.We find similar statements both in Kakyō and its first draft, Kashū no uchi nukigaki. Concerning the plays meant to be the opening act of a Noh program （the first and the second play）, which correspond to“ ōyōnaru Nō”, it is stated that they should have an especially legitimate source. As for the plays in the middle of the program（from the third on）, they“must shift the straightforward style of the opening plays towards a more detailed, subtle direction”. We conclude that the rank of a Noh does not only influence what kind of performance should the actor aim for, but it is also decisive on what stage of a day’s Noh program should that play belong to. The purpose of this research is to compare the features of “ōyōnaru Nō” and “chiisaki Nō” on hand of Zeami’s treatises and to consider the implications of such differentiation of Noh plays.