The arguments both for and against soul theory are worthy of consideration but I am going to argue that the there is more evidence for soul theory than there is evidence against it. Since the soul is something that cannot be measured, one is required to abstractly consider the nature of a soul to argue for its existence. The counter argument, which I will label the reductionist approach, to soul theory says every faction of the human being can be explained through physical properties (which can be measured) and that there is no room for soul theory.
For my position, I will propose that a few things can indeed be known about the nature of the soul and then present the premise of the soul as a necessity for biological existence.
If the soul exists and it cannot be measured, that seems to indicate that it’s existence is not a physical property. As the brain is not yet able to comprehend non-physical existence, it is necessary to provide some basis that non-physical things can exists (destroying any reductionist type argument in the process). The first and most obvious is gravity. Gravity is a property which exists and is demonstrable at will so long as matter exists. Another, is magnetic fields which also affiliate with something material. However, there is one example which does not seem to be bound to matter, energy. Again, since the brain is not capable of non-physical observation, we only know that energy can be found as a derivative of some physical process. But what about quantum fluctuations? For the ‘big bang’ to bang, an enormous amount of energy was needed, energy that is still identifiable today. Since nothing existed a split second before the ‘big bang’ it is reasonable to assume that the energy necessary already existed independently of matter or it came from somewhere. In either case, energy would have to exist or come in to existence in the space between something and nothing, the non-physical. With this understanding of non-physical dimension, we can further extrapolate. If this dimension does exist, and non-physical things like gravity, magnetic fields, and energy hold their reasons for existence inside this dimension then why not other non-physical things like thoughts or instincts/emotions? Indeed, that is the position I will maintain. It follows then, that if I hold the soul exists and is non-physical, then it must exist in this non-physical dimension where other non-physical substances exist. Substances like thoughts, instincts/emotions, energy, etc. That is the correct supposition, but not the entirety of it. To exist in the physical dimension, parts of the non-physical dimension are necessary. Since both physical things and non-physical things exist, and non-physical things are necessary for physical things to exist (quantum fluctuations) it is easy to suppose the sum of the things that exist in physical dimension (universe) are in some correlation with the things that exist in the non-physical dimension (non-physical universe). However, I do not feel it is adequate to assume there is such a correlation as at this point science suggests the universe is actually expanding. If the universe is expanding, then additional matter is being borne from something. I would submit it is from the substance of the non-physical dimension thereby implying the non-physical dimension is unscalable if not infinite. The corollary question then is how does something like a soul which exists potentially in an infinite domain, correlate with living beings who are finite? With this question we can further expound on the nature of the soul. We know certain things like thoughts, instincts/emotions, and energy (non-physical properties) are necessary to describe any facet of biological existence (the living-physical). That can only mean that the soul is the combination of the non-physical properties in any living-physical being. Since every living-physical being carries such properties, it logically follows that every living-physical being also has a corollary soul. As suggested in this argument since non-physical substances presuppose physical substance, non-physical properties therefore presuppose physical properties, i.e. the soul is a necessary presupposition of the living-physical being.