In philosophy of mind, monism is usually contrasted with the dualist position that mind and matter are deeply different. Thus, monism is the claim that mind and matter are essentially the same.
Spinoza was preoccupied with the central problem of the Cartesian inheritance, viz. that of accounting for the apparently systematic causal interaction between mind and body. This problem had arisen for Descartes specifically because he had believed that mind and body were discrete types of substances with irreconcilable natures. Contra Descartes, Spinoza denied that mind and body were separate substances at all, and proposed instead that they are merely separate attributes of a single substance. He suggested that, for every physical item P, there is a corresponding mental item I(P), which he identified as “the idea of P.” The human mind, for example, was nothing for Spinoza but the “idea” of the human body. These “ideas” differ from one another in “perfection,” based upon the complexity of the physical object to which each corresponds.
As you know, we have our own interpretation of parallelism in a nihilist context
There are many monisms. What they have in common is that they attribute oneness. Where they differ is in what they attribute oneness to (the target), and how they count (the unit). Thus, strictly speaking, there is only monism relative to a target and unit, where monism for target t counted by unit u is the view that t counted by u is one.
Monisms contrast with pluralisms and nihilisms. Where the monist for target t counted by unit u holds that t counted by u is one, her pluralistic counterpart holds that t counted by u is many, and her nihilistic counterpart holds that t counted by u is none. (Dualism is a special case of pluralism: the dualist holds that t counted by u is two.)
To illustrate, let the target t1 = the category of concrete object, and let the unit u1 = highest type. To be a monist for t1 counted by u1 is to hold that concrete objects fall under one highest type. The materialist, idealist, and neutral monist are all monists of this sort (substance monism). They all agree that concrete objects fall under one highest type, disagreeing only over whether the one highest type is material, mental, or something deeper.
To be a pluralist for t1 counted by u1 is to hold that concrete objects fall under more than one highest type. The Cartesian dualist is a pluralist of this sort (substance dualism). She holds that concrete objects fall under two highest types, specifically the material (with the primary attribute of extension) and the mental (with the primary attribute of thought).
To be a nihilist for t1 counted by u1 is to hold that concrete objects fall under no highest type. The bundle theorist who is an eliminativist about concrete objects would be a nihilist of this sort (substance nihilism). This sort of bundle theorist denies that there are any concrete objects, maintaining that there are just bundles of compresent properties.
This is consistent with our view of nihilism: there is no inherent high level to both matter and form, but they are governed by parallel patterning laws, much like a parallelism which does not require a single origin but acts through indirect, parametric limiting forces.
Melissus, an eminent citizen of Samos and admirer of Parmenides produced a book approximately 50 years later, rendering Parmenides' doctrines in clearer prose. In the following excerpt he explains the canon of infinity and perpetuity of the One: "Since what comes into existence has a beginning, what does not come into existence has no beginning. But what exists has not come into being. [which was deducted before in the text] Therefore it has not got a beginning.
Again, what is destroyed has an end, and if something is indestructible it has no end. Therefore what exists, being indestructible, has no end. But what has neither beginning nor end is in fact infinite. Therefore what exists is infinite. If something is infinite, it is unique. For if there were two things they could not be infinite but would have limits against one another. But what exists is infinite. Therefore there is not a plurality of existents. Therefore what exists is one." (Simplicius, Commentary on the Physics, 103.13)
The above states the gist of classical monism.
This affirms the singularity of order. And then:
Monism, because it describes a belief in one substance, can be used in two distinct ways:
• To describe the view that only matter, or the physical body, exist.
• To describe the view that only mind, or spirit, exist.
The first option is called "materialism" or "physicalism"; the second option is called "idealism" (which you may remember from our discussion of Berkeley in TOK).
This is where ANUS-style parallelism comes in: the organization of matter, energy and ideas is the same. This is idealism that encompasses materialism.
And finally, the soundbite version:
Monism is any philosophical view which holds that there is unity in a given field of inquiry, where this is not to be expected. Thus, some philosophers may hold that the Universe is really just one thing, despite its many appearances and diversities; or theology may support the view that there is one God, with many manifestations in different religions.
It seems to me metal is inherently monist, or believes that the organization of matter and ideas is based in context, not the things-in-themselves. In simpler terms, the cause of all things is the interreaction of forces that produces the pattern of the world.
In the monist view, there may actually be stages of life which are determined not by that which acts but by the context which created it. Humans hate this viewpoint because it implies they did not create and do not regulate their own consciousness.
In other words, a chair is not inherent (dualism: another pure world exists where the form of chair is defined) but it is the simplest design to adapt to our context, in this case the interaction between gravity and the human form.
However, it is the best viewpoint for epic surveys of history across thousands of years... patterns develop in the herd, and come to fruition in ways where we are just the actors doing what history has made convenient to us.
While we may believe
our world - our reality
to be that is - is but one
manifestation of the essence
Other planes lie beyond the reach
of normal sense and common roads
But they are no less real
than what we see or touch or feel
Monism is the most ancient philosophy of transcendentalists, and one that returns as science, exhausted with separating meaning from form, finds its answers crumble in its hands. (Science could accept monism, but this challenges Rationalism -- a future topic).