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Monday, February 23, 2026

Spinoza and the double-aspect theory


If you have read my last blog, you may have noticed that I defend there a view about the relationship between mind and body that is called the double-aspect theory, or also dual-aspect monism. I came to this view long ago when I was working on my PhD thesis and didn’t know yet its name, or that it was, for example, Spinoza’s view on reality. My question then was methodological: What is the difference between the methods of explanation and understanding, especially when we study human behaviour and actions? My answer was that the method of explanation asks for the causes why someone does what he or she does, so for the causes of behaviour, while the method of understanding asks for the reasons why someone does what he or she does, so for the reasons of actions. In other words, the method to be used depends on the kind of questions we want to ask about a human. I’ll not repeat or summarize here my PhD thesis, but in view of my present ideas, we can say that with the method of explanation we study the human body and with the method of understanding we study the human mind. So, if we want to know why someone does what he or she does, we try to explain it if we want to investigate the causes that made someone’s body move in a certain way, and we try to understand it if we want to investigate the mental reasons that made someone perform an action. We can also say that there is one substance “human being” but we can approach it as a physical entity or as a mental entity; as a body or as a mind. Body and mind (or the mental) are the two basic aspects of a human being.
Seen this way, my version of the double-aspect theory is epistemic, and actually it says nothing about the ontic side of humans, but without substantiating this view, I also think that ontologically there is only one substance, and not two substances like a body substance and a mind substance that are mixed in such a complicated way, for instance, that we could investigate them only by seeing them as aspects. As I indicated in my last blog, I see body and mind rather as structures of the one existing substance that basically makes up the world; a bit like that the ink in a book can be structured that way that it is the text of a story at the same time. The text is a manifestation of the substance.

I don’t know whether there are older versions of the double-aspect theory, but this view on reality was central in Spinoza’s philosophy. By developing his version of substance monism, Spinoza criticized Descartes’ mind-body dualism, which says that body and mind are different substances that make up humans and that interact in the brain. According to Spinoza there is only one substance that makes up the world.
How should we conceive such a substance? That’s why Spinoza introduced the concept of attribute. As defined by Spinoza it’s a difficult concept, but following Beth Lord in his Spinoza’s Ethics – which is a guide to Spinoza’s Ethics – we can say that “attributes are the different ways in which a substance can be perceived. ... An attribute is the substance itself, as perceived in a certain way” (p. 21; italics Lord). According to Spinoza, two attributes are relevant for humans: extension and thinking. Also for Descartes extension and thinking are relevant for humans, but for him they are separate substances, while for Spinoza extension and thinking are two different attributes of the one substance that exists in this world.
Once we know this the analogy between Spinoza’s world view and the double-aspect theory is clear, especially when we use its alternative name “dual-aspect monism”: Spinoza’s attributes are nothing but what I have called aspects and his attributes extension and thinking are what in dual-aspect monism are called matter and mind. The latter are called body and mind when we talk about humans.
At the end of my last blog I remarked that there may be more aspects than the two aspects matter and mind. This is what Spinoza actually says, too, for according to him the one existing substance has an infinite number of attributes. In my terms this means that the one existing substance has an infinite number of aspects. In fact, Spinoza’s theory is a multi-aspect theory, but because only two attributes are relevant to humans, we can ignore it.

5 comments:

Paul D. Van Pelt said...

I always loved the double entendre of the wine glass and profile super -imposition. Am not that versed on Spinoza, his theory, or how he and Descartes differed. Not that important to me. How we view things falls upon several notions, near as I can tell. First, maybe, is: intention, which emerges from the contextual reality notion and interests, motives and preferences, (impishness). There are, most always, different ways of seeing the same thing.
Contextual reality dictates that people view and hold interests, motives and preferences in different ways, baseline-dependent on their intentions. This is little more complex than the goblet/profile superimposition.
It only seems to be . Things ARE as they appear. Intentions alter that landscape, somewhat.

HbdW said...

Thank you for your thoughtful comment, Paul. I think that what Spinoza discusses in his body-mind theory and what you bring forward are on different levels. In view of the discussions in the Netherlands and elsewhere in the 17th century, what Spinoza had in mind was, among other things, the theological problem what the relation is between body and soul/mind/spirit. Descartes, as a good catholic, meant that body and soul were two different substances that had contact via the pineal gland in the brain. Spinoza (seen as an atheist by many contemporaries) rejected this view and said that body and soul are one. What I wanted to do in this blog is interpreting it as a version (or forerunner) of the double-aspect theory. I always try to find or make a picture or take a photo that is relevant to my blog. The best one I found was the wine glass and profiles figure (I wasn’t creative enough to take photo that fitted this blog).
But how relevant is all this for our daily activities? Sometimes it is, often it is not (at the background at most). And as I see it, your questions refer to these daily activities. For me then, indeed, intention is a central notion, and intentions cannot be considered without the context.
As for me, things are for us as they appear for us. Can we know how things “really” are. My idea just expressed can only mean that we can only agree on what there really is (intersubjectivity) but we never know whether we are right.

Paul D. Van Pelt said...

Well discussed and explained! My ideas and thinking did not materially factor in belief, faith and religious position. I did not know enough about either Spinoza or Descartes to fully think this out. Certainly, their differences made a difference in their view of things. It is a bit like the study of philosophy, itself. There is doubt and uncertainty, and, "...we never know whether we are right."
Thanks for setting me straight.

Paul D. Van Pelt said...

Today is Thursday, February 26, 2026. My Internet connection is clunky, as it often is. I read your random quote this morning. Read it twice---was unsure of context. Did you mean infinitely or indefinitely? The intention of the quote suggests *infinitely* as the modifier---unless I have missed something? Just asking, see. I was reminded, via radio, that Spring IS coming. I'm infinitely glad for that! Well, that is not conrextually valid, really. Infinity is neither place, nor position: You can't get there from here, because there is no "there" there. I think Feynman; Hawking and Searle would agree, although I am only contextualizing---more or less. Sure. Thanks!

HbdW said...

Thank you for your comment Paul. Malthus wrote "indefinitely".