 Another common reason for denying souls to plants is that they are not capable of locomotion, of changing their position, as humans and animals are (Nanna: 41, 71). But why should motion to different places be necessary for life?, Fechner asks. Plants move too, its just that they move vertically rather than horizontally. One maintains that the movements of plants are not voluntary, like that of humans and animals, because they are subject to physical necessity. But Fechner replies that the actions of animals too can be shown to be physically necessary. The mere necessity of an action—its explicability according to mechanical causes—does not show that it cannot be also accompanied by internal or mental events (Nanna: 79). 