One of the most famous claims of Spinoza’s metaphysics is that there is only one substance – only one real ‘thing’ – and everything else is a ‘mode’ of that.
‘Mode’ here means something like a property, an action, a relation, that in some sense don’t ‘really’ exist, or don’t exist ‘in themselves’, but only by being the property, action, or relation ‘of’ something else.
The claim appears to be that just as my right-handedness is not a ‘thing’ but rather a property of me, I am not a ‘thing’ but a property of ‘God’ (or ‘Nature’, ‘Reality’, etc).
A lot of people have found this claim absurd or incomprehensible. For instance, Edwin Curley protests that “Spinoza’s modes [people, houses, cars, oceans] are…of the wrong logical type…for they are particular things, not qualities…When qualities are said to inhere in substance, this [means] they are predicated of it. What it would mean to say that one thing is predicated of another is a mystery that needs solving.”
But I think this is wrong. Far from being mysterious or implausible, the idea that particular things, including us, are modes of a single substance is the most reasonable position when the topic is considered carefully. At the same time, I think this idea is also very counter-intuitive, rather disturbing, and seriously embraced by relatively few people. As such, it is exactly the sort of idea you’d expect to find in the writings of some sort of philosophical genius…
Now, if we are modes, we are complex dynamic modes, not static simple ones, so the usual examples (properties like ‘redness’) are a bad model. A better example is a ‘gait’ – running, walking, trotting, galloping. Now on the one hand, we do sort of speak of gaits as ‘things’ – for instance, the same gait can persist, can be identified at different moments. And it can have do things – we might say ‘the horse’s gait caused it to trip over’.
But on the other hand, we don’t think the gait is really a ‘thing’ – if someone pointed at a trotting horse and a horse lying down and said there were ‘three things: two horses and a gait’ we’d think them very confused. Moreover, a gait without a horse is like a grin without a cat – nonsense.
This is because the noun ‘gait’ does something quite useful – it ‘abbreviates’ the way that the different parts of the gait interact. The gait ‘contains’ multiple particular actions (a straightening of a leg, a contraction of a muscle, etc.) and these interact in a complicated way that serves quite effectively to maintain the gait.
So to avoid going over every detail of this process, so we summarise it by talking about the ‘gait’ as something that persists and preserves itself from one moment to the next. But it’s still only a complex mode, an action performed by the horse and its legs.
Note that this doesn’t change if the particular leg involved changes. An unsteady person hopping, who switches from one leg to the other, might be said to have one enduring gait, instantiated first in one leg and then in the other. But this wouldn’t make the gait any more a substance.
Now, Spinoza’s claim can be made in two stages here. The first stage is to say that just as a gait is a complex action performed by a horse, so a horse (or a human) is a complex action performed by matter.
For a horse to exist is for certain organs and tissues to interact with each other in certain ways; for a tissue to exist is for cells to interact in certain ways; for a cell to exist is for certain molecules to interact in certain ways; and for a molecule to exist is for certain fundamental particles of matter to interact in certain ways.
So when we say that a horse ‘exists’, what we really mean is that certain particles (whatever you think particles are) are interacting in a certain way – for matter to do certain things.
And there’s the same asymmetric logical dependence – matter without a horse is perfectly possible, whereas a horse without any matter is meaningless nonsense (notwithstanding the philosophers who have endorsed it).
And just as with hopping, the fact that ‘the same horse’ can persist while replacing some matter with other matter (e.g. by drinking and sweating) doesn’t stop it from being a complex act performed by matter.
Similarly, even though the interactions between these parts are mind-bendingly complex, and incommunicably important, this just makes it overwhelmingly handy to speak as though ‘a horse’ is a substance (notwithstanding the immense amount of philosophical ink spilt on trying to obfuscate this point).
So I would argue that the idea of humans and horses being complex actions performed by – ‘modes of’ – matter is the most reasonable position to take, whatever Spinoza says. But he makes a further claim that is more speculative.
We spoke of ‘matter’ as implicitly something with parts – there are multiple bits of matter, and they are all really distinct from each other, all separate ‘substances’. But Spinoza says that these too are really modes, actions taken by God. So rather than you and I being ‘things that matter does’, we are ultimately ‘things that God does’, where ‘God’ means the universe considered as a single, indivisible whole.
His arguments for this are complex and technical and I’m not too sure I understand them but I’ll just say that it’s not itself is not inherently implausible that different acts of the same thing could be mistaken for separate ‘parts’ of it is perfectly intelligible – imagine, for instance, a hitmonchan punching four opponents so fast that a dull-witted observer is made to think it has four arms. Spinoza’s claim is that in relation to ‘God’, we are just like that dull-witted observer or pokemon.