I came across an article written by Michael Shermer in 2004. He is a well-known author and columnist for the Scientific American magazine. In that article he gives a definition for monism:
“Dualists hold that body and soul are separate entities and that the soul will continue beyond the existence of the physical body. Monists contend that body and soul are the same and that the death of the body — the disintegration of DNA and neurons that store my personal information — spells the end of the soul.” 
I read and re-read the paragraph multiple times. I have never heard of this definition of monism before. This is not monism! He is giving us the definition for materialism. I have to add that his definition of dualism is not the commonly accepted definition of dualism either.
The Wikipedia article  on monism is one of the best that the collective wisdom has produced. I am pleasantly surprised by the clarity of the Wikipedia article. In contrast, the SEP article  on monism is very terse and not comprehensive at all. One expects comprehensive articles from SEP. One criticism of the Wikipedia article is that it does not discuss the “Unity of Being” (Absolute Monism).
I will take this opportunity to mention the major lines of thought in monism and compare them to my version of monism which I call the Soul Monism . I will ignore purely analytical/academic or mathematical versions of monism.
Soul never dies
Before I change the tone of this article to philosophical I would like to stress a spiritual fact: soul never dies. The individual mind dies, the body dies but the soul never dies.
Monism does not say that soul, mind and body are the same. It is clear that they are different. Monism says that soul, mind and body were the same in the beginning and they will be the same in the end.
Soul, mind and body are different transformations (emanations) of the singular Cosmic Soul. The entire Cosmos is an expression of that singular soul.
This is the most popular and rational line of thought in monism. In one of his panel discussions the famous philosopher David Chalmers said that he is partial to panpsychism. I also think that panpsychism has a lot of merit. Many philosophers of academic metaphysics are leaning towards panpsychism.
“In philosophy, panpsychism is the view that mind or soul is a universal feature of all things. Alternatively, it is the view that all things have a unified center of experience or volition. Panpsychism is one of the oldest philosophical theories, and can be ascribed to philosophers like Thales, Plato, Spinoza, Leibniz, Schopenhauer and William James. Panpsychism can also be seen in eastern philosophies such as Vedanta and Mahayana Buddhism. During the 19th century, Panpsychism was the default theory in philosophy of mind, but it saw a decline during the latter half of the 20th century with the rise of logical positivism. The recent interest in the hard problem of consciousness has once again made panpsychism a mainstream theory.” – Wikipedia 
My understanding of panpsychism is that Consciousness is immanent in all entities. Please see  for the definition of Consciousness. Soul Monism  also says that Consciousness is immanent in all entities but adds many clarifications. Regarding immanence and transcendence Soul Monism states that
- When viewed from the perspective of the soul, Consciousness is immanent.
- When viewed from the perspective of the mind, Consciousness is transcendent.
Note that Consciousness (“C” is capitalized) is not referring to the waking consciousness, awareness, or perception. Consciousness is not referring to the cognition either. Consciousness (“C” is capitalized) refers to the indescribable ultimate reality.
“Dialectical monism, also known as dualistic monism, is an ontological position that holds that reality is ultimately a unified whole, distinguishing itself from monism by asserting that this whole necessarily expresses itself in dualistic terms. For the dialectical monist, the essential unity is that of complementary polarities, which, while opposed in the realm of experience and perception, are co-substantial in a transcendent sense.” – Wikipedia 
There are analytical philosophers saying that it depends on how we count. If we count “all” as “one” then we can call it monism too. Ontological monism objects to this simplistic thinking and clarifies that there is unity behind multiplicity. Ontological monism claims that multiplicity emerged from a singular essence. The unity behind multiplicity is real (ontological).
Soul Monism is ontological monism. Soul Monism does not deny the reality of multiplicity but claims that multiplicity is derivative. The derivative or relative truth concept was examined in great detail by Shrii Shrii Anandamurti.
Unity of Being = Absolute Monism
Unity of Being and Absolute Monism refer to the same concept. There is only ONE Absolute Being in existence. Cosmos including all the physical universes and the infinite number of souls are transformations or internal reflections of this Absolute Being which is also known as Consciousness (Puruśa in Sanskrit).
In Sufi metaphysics the Unity of Being is known as Wahdat al-Wujud. Ibn Arabi (1165 – 1245) is often cited as the originator of the concept of Unity of Being but this concept existed since Shiva’s time 7000 years ago. We see the same concept being taught by Tehuti 6000 years ago in Egypt.
Soul Monism is absolute monism. Soul Monism brings clarity to the main concepts of absolute monism. For example, it explains what “transformation” and “internal reflection” mean .
Pantheism, Panentheism, and Unity of Being
The term Pantheism means “All is God” while “Unity of Being” emphasizes that there is just a single being in existence and this single being is God. However, “Unity of Being” may be closer to Panentheism, because Panentheism states that while the Cosmos is part of God or God’s mind, God is still greater than his creation.
Commentary on Dialectic Monism
The definition of “Dialectic Monism” does not sound so bad! In fact, it sounds very much like the Ananda Marga definition of monism. This is interesting because Ananda Marga Monism is ontological monism obviously but it is also absolute monism. I thought it would be interesting to quote from the “Philosophical Treatise of Ananda Marga” which is a text of only 17 paragraphs.
“Nirguna and Saguna are two aspects of one and the same Brahma. They are not two different Brahmas. It should be clearly mentioned that Ananda Marga is absolute monism – it is not dualism. A question may arise: How can Ananda Marga be called monism when it declares that Shiva and Shakti are separate entities. The answer is that in Ananda Marga philosophy, Shiva, or Cognitive Force, is both the material and the efficient cause, whereas Shakti, or Operative Force, is only the efficient cause. Shakti is merely subservient to Shiva, Shakti has no existence separate from Shiva. So we can safely conclude that Ananda Marga philosophy is based on monism.”
Even though the Ananda Marga Monism sounds very much like the Dialectic Monism it is not the same because the Ananda Marga Monism does not accept the “complementary polarities” as equally substantial. Ananda Marga philosophy clearly states that the cognitive aspect (Consciousness) of the Absolute Being (Godhead) is primary