Like Descartes, Berkeley is a metaphysical dualist. But unlike Descartes, Berkeley did not subscribe to a dualism of mind and body but instead developed a unique and robust metaphysical distinction between the realm of ideas, on the one hand, and the realm of spirits, on the other. Rather than follow Descartes in separating the world into that which is material and that which is mental, Berkeley cashes out his distinction in terms of passivity and activity. Ideas, he says, are purely passive entities, while spirits, such as our own mind and God’s, are purely active. Commentators are broadly in agreement on these fundamentals of Berkeley’s ontology. Where there is lively disagreement, however, concerns how we are to interpret Berkeley’s theory of the causal relationship between these two ontologically distinct realms.
In his paper, “Berkeley on the Activity of Spirits”, Sukjae Lee defends an interpretation that attributes to Berkeley the view that human beings enjoy a “dual power” to causally produce two types of distinct output. When we are engaged in willing, we produce volitions which are purely spiritual. When we are engaged in imagining, on the other hand, we are responsible not only for the production of volitions but also for the production of ideas, namely ideas of imagination, which are the effects of prior volitions. Thus, on Lee’s reading, although all of our causal activity originates in the spiritual realm and has, as we might say, spiritual ‘input’, the ontological status of the output of our activity may be either spiritual or ideal, depending on whether it is a volition or an imagining. As Lee puts it,
[W]e have the power to produce volitions, and this power comprises the inner core of our activity in such a way that, even if we were to possess just these powers, we would be genuinely active in virtue of them. But, as it turns out, we are directly aware that, in the case of ideas of imagination, our volitions result in the actual production of the ideas, such that we can claim this power to produce ideas of imagination as well. (p.27)
Lee positions his dual power reading in opposition to Pitcher’s more restrictive ‘single power’ assessment of Berkeley’s theory of human causality. Although Pitcher does not dispute that Berkeley himself thought that the human mind was causally responsible for the production of volitions and the ideas of the imagination, Pitcher tries to make the case that Berkeley “should drop this additional claim that ‘image-volitions’ are the true active causes of their intended effects [I.e. ideas of imagination]” (p.26) because according to Berkeley’s own metaphysics the spirit does not enjoy the ability to directly perceive its own powers. Since the mind has no means of perceiving itself, it has no image of its powers and so no means of knowing whether it is responsible for the images that appear to follow from or accompany its volitions. The problem with this line of argument, Lee suggests, is, for one, that it flies in the face of many passages where Berkley carefully spells out that although the mind has no imagistic knowledge of itself (it being by nature active) it still can “know [itself] by a certain internal consciousness” and through an “inner feeling” or simply through “reflexion” (p.26). Furthermore, it seems that this argument would also have to render the mind’s capacity to know that it has the power produce volitions equally obscure and so equally problematic (p.27). But this is not a move that Pitcher wants to make since he still wants to preserve the single power story.
Someone more sympathetic to Pitcher’s analysis may want to uphold the single power reading by grounding it in an alternative factor that does not rely on Pitcher’s ‘obscurity argument’. The factor I have in mind is the input-output distinction between willing and imagining mentioned above. Simply put, it is because imagining is a two-step process involving input from one ontological realm and output from another that it should not be treated on the same terms as willing, which is a one step-process. Witness that when I will, there is no clear distinction between the act and its product; the volition is the willing. But conversely, when I imagine something, I must first will to do so and then have my volition confirmed or ‘registered’ in the mind’s eye as an idea.
It seems that this is enough to establish the right kind of distinction between acts of will and acts of imagination that Pitcher needs in order to lend the single power story he favours more credence. For while there is no room for an external causal source, e.g. God, to get a wedge in, so to speak, between my volition-as-act and my volition-as-product, it seems that there is ample room for God to have so structured the world that my volitions are succeeded by opposing images, random images or indeed no images at all. Thus, a defender of Pitcher might reason, Berkeley should not have attributed the kind of dual power causality to human beings that Lee’s paper endorses.
 ‘Single power’ is not Pitcher’s term.