First Substance is something 'standing on itself'. It is physically generated from an initial condition:the elements of the dynamical system, plus the dynamical law (going to be the Essence of the first substance in question) inherent in those system elements. This first substance, as it stands, is a (unique) collection of properties. Each property is, as a property, not ' standing on itself ', because it always is a propertyof some first substance. They are in a way beings but they are not (self)subsistent. These 'beings' are calledaccidents. But they need not always to beaccidental. Some accidents are directly caused by the essence of the thing, others are caused by extrinsic (extrinsic in relation to the Essence) factors.First Substance is something 'standing on itself'. It is physically generated from an initial condition:the elements of the dynamical system, plus the dynamical law (going to be the Essence of the first substance in question) inherent in those system elements. This first substance, as it stands, is a (unique) collection of properties. Each property is, as a property, not ' standing on itself ', because it always is a propertyof some first substance. They are in a way beings but they are not (self)subsistent. These 'beings' are calledaccidents. But they need not always to beaccidental. Some accidents are directly caused by the essence of the thing, others are caused by extrinsic (extrinsic in relation to the Essence) factors.The first substance itself is situated in the fenotypical domain and is the totality of its properties which are also situated in that same domain. If we speak in the context of predication, then we can say that the First Substance is never in a subject, and as a predicate can never be predicated of a subject, while the Second Substance is always in a subject (this subject is the first substance), and as a predicate can be predicated of a subject. Accidents also are always in a subject, but, in contradistinction to Second Substance, accidents belong to the fenotypical domain.In the philosophy of Aristotle and St Thomas Aquinas a distinction is made between First Substance and Second Substance.I. The obvious division of things into the stable and the unstable, the more or less independently subsistent and the dependent, oressentiallyinherent, appears beset with obscurity and difficulty as soon as it is brought under reflective consideration. In their endeavour to solve the problem,philosophershave followed two extreme tendencies. Some have denied the objectivity of thesubstantialor noumenal element, and attributed it wholly or in part to themind; others have made the phenomenal or accidental element subjective, and accorded objectivity tosubstancealone. These two extreme tendencies are represented among the ancientGreekmaterialistsandatomistson the one hand and the Eleaticpantheistson the other.Aristotleand hismedievalfollowers steer a middle course. They hold to the objectivity both ofsubstanceand ofaccident, though they recognize the subjective factor in the mode of perception. They use the termaccidentto designate anycontingent(i.e.nonessential) relation between an attribute and its subject. As such it is a merelylogicaldenomination, one of the five predicables oruniversals, modes of systematic classification genus, difference,species,property,accident.In this sense it is calledpredicable, as distinguished frompredicamental,accident, the latter term standing for areal objectiveformor status of things, and denoting abeing whoseessentialnatureit is to inhere in another as in a subject.Accident thus impliesinexistenceinsubstancei.e. not as the contained in the container, not as part in the whole, not as a being intimeor place, not as effect incause, not as theknownin theknower; but as an inherent entity or mode in a subject which it determines.Accidents modify or denominate their subject in various ways, and to these correspond the nine "Categories":