Please don't misunderstand - I was not trying to be condescending. I always enjoy listening to someone try to tell me what a soul is - I've heard so many different answers when I ask the question.
However, all I read in that post was a lot of Sophocles-esque reasoning, a lot of circular reasoning, and a lot of things that just did not make sense. The soul has the power to gain nutrition? How, exactly. The power to gain nutrition is in the cells of our small and large intestines. What is a "vegetative soul" exactly? And when you were talking about a soul being a form of something (your chair and dog analogy) it sounds to me as if you were just pointing out that dogs look like dogs because they're dogs. That makes no sense. Dogs look like dogs because they have 42 chromosomes, and on those chromosomes it tells each cell what to differentiate into (hair cells, liver cells, eye cells, olafactory cells, etc). Chairs look like chairs because they have been made in a factory. People look like people because they were conceived using 23 chromosomes from their mother and 23 chromosomes from their father. Every single thing that makes a person look and act like a person is written on the DNA found on those chromosomes.
It would a be a stretch to say that I misunderstand you. Asking me the weight of and telling me that there is no organ of the soul ? You either believe me to be an idiot or to have idiotic thoughts. As stated before, let's all at least pretend we can have an adult conversation without all the ad hominem.
As for Platonic forms, every object has a form which allows us identify them and differentiate them from other objects. The form of the chair, for example, is our conceptual understanding of what a chair is: something on which we sit. That is, in a way, what makes a chair, a chair. Of course a chair has other attributes such as its material, it's construction, etc. which differentiate it from other chairs but the form is solely its essence. Plato calls the forms in living things souls. So the form, or in this case that which we call the soul, a plant involves it taking in nutrition and growing. How it does this is, as you stated, by it's physical constitution and processes, but the how is not the concern of the form, only the what. And the what is that all plants take in nutrition in order to grow and therefore that is part of its form. That is part of the essence of being a plant. Above that, we have the form of the animal, and then the form of the human. Each describing the essence of what the animal and the human is, respectively.
Please note that I have not yet asserted of the soul as defined by Catholicism. The soul, until now, is nothing more than that which makes a human, human. That is, you cannot refute it because it is merely a set definition which, until this point. All I have done is laid out what a form is, that the form is called the soul in a living being, and that a form is the essence of its being. The essence if human being, as you stated, involves sequences of chromosomes among other things, all these together constitution the human form, or soul.
With that said, from this point forward, I shall refer to the Catholic conception of the human soul when I use the word. The soul is largely, as far as my understanding on the matter goes (which is admittedly amateurish), what differentiates us from animals. So in order to describe the human soul, a logical place to start would be to articulate the differences between the human and the animal forms. Allow me to put forth a few for your digestion:
First, we are acquainted with abstract objects (sets, propositions, numbers, properties, etc.). Material entities cannot be acquainted with immaterial entities. Therefore there is some immaterial principle of knowing. This is what we would define as the soul.
Second, we make free choices. A choice is free only if it is not caused, that is, if there are at least two possible worlds that are identical to the point at which the choice is made, but each of which contains a different choice. The physical world is deterministic, wherein there is a chain of causation, the principle of choosing cannot be physical. This choosing thing is the soul.
What you seem to be overlooking is that we are not imposing on man this thing called a soul but rather we identify these aspects about man and identify the operating principle of these aspects the soul. Thus it is not an imposition of a construct but it is an identification of what is. We note what is in the human construct and denote some of that to be the soul, or that which holds the faculty to perform the functions I asserted above.
