Whether walking, standing, sitting, lying, or rising, he should practice both 'cessation' and 'clear observation' side by side. That is to say, he is to meditate on the fact that things are unborn in their essential nature; but at the same time he is to meditate on the fact that good and evil karma, produced by the combination of the primary cause and the coordinating causes [i.e., he is to practice 'clear observation'], he is also to meditate on the fact that the essential nature [of things] is unobtainable [by intellectual analysis].
From The Awakening of Faith, p. 101