The human person's personhood, is rooted in his spiritual dimension which in the thought of St. Thomas Aquinas, of which the spirituality constitutes the very core of the human person unlike no other created creature. It is from this core springs all of man's intentions, thoughts and motives and feelings, rational or irrational.
Although, it could be said that man tends to share the vegitative and sentient faculties and indeed, operations with plants and animals, but it remains that such faculties and operation cannot be reduced to the level of plants or animals. The reason is deduce from the fact that man's operations are grounded in the spiritual and rational nature of man. The same is true that because of man's spiritual dimension, the human person cannot be reduced to the level of things or object, and indeed animals,no matter the rededfinations for whatever outrageous reason, and of course, any such attempt, although, understandable but unacceptable.
The Thomistic principle is of the view that man's subjectivity implies man's irreducibility to the level of animal or things. The reason stern from the very fact that man is not just a sample of nature because of his special place in the order of created beings. The spiritual dimension of man which is the core of his being, unlike no other created being, is not just a pure spiritual subject, but a concrete subject that incarnate his inner self through his body.
Accordingly, the human person is a concrete "I" which is existing and acting. The same is true, that as a concrete subject, his concrete experience, is endowed with specific subject and concrete "I" that is nonrecurrent and unique none comparable to any created being.
Only human person is unique and unrepeatable subject who possess and dominate himself and determine his own existence. Therefore, a person is self subsistence, which means he is self_ oriented, self_purposed, and indeed, an end to himself, a being with absolute value like no order, in the order of created creature. In addition, a person has dignity of his own, not bestowed on him by another, with inviolable and incommunicable and absolute right that are not subject to negotiation; the right and freedom of responsible, self creation and self fulfilment.
It is through the spiritual dimension, that human person becomes aware of himself and possess himself because the spiritual essence enable him to master himself as he become self- manifesting, self _ communicative and self _ sharing and self_ given. The same is true that in this dimension, the human person is self-transcending, as he transcend himself and go beyond all what is relative and temporal to relate with the absolute and eternal. The human person capacity for intense self possession, expresses itself in a conscious, free and self creation.