Form (Lat. forma, by transpose from μορφή) is defined by Aristotle as λόγος τῆς οὐσίας, the doctrine of the substance or essence of a thing. "A trumpet may be said to consist of two parts, the matter or brass of which it is made, and the form which the maker gives to it. The latter is essential, but not the former; since, although the matter were silver, it would still be a trumpet, but, without the farm it would not. Now, although there can be no form without matter, yet as it is the form which makes the thing what it is, the word form came to signify essence or nature" (Fleming, s.v.). The Scholastics distinguished form substantial from form accidental. Substantial form they defined as actus primaries una cum materia constituens unum per se; accidental forms as actus secondarius constituting a unit per accidens. The unit of being composed of soul and body was defined to be of the former sort. Form, according to the ancient definitions, is therefore necessary to matter; absolutely formless matter is inconceivable. Lord Bacon (Nov. Organ. 2:17, says: "When we speak of forms, we understand nothing more than the laws and modes of action which regulate and constitute any simple nature, such as heat, light, weight, in all kinds of matter susceptible of them; so that the form of heat, or the form of light, and the law of heat, and the law of light, are the same thing." Also (Nov. Organ. 2:13), "The form of a thing is the very thing itself, and the thing no otherwise differs from the form thane as the apparent differs from the existent, the outward from the inward, or that which is considered in relation to man from that which is considered in relation to the universe." "The sense attached at the present day to the words form and matter. is somewhat different from, though closely related to, these. The form is what the mind impresses upon its perceptions of objects, which are the matter; form therefore means mode of viewing objects that are presented to the mind. When the attention is directed to any object, we do not see the object itself, but contemplate it in the light of our own prior conceptions. A rich man, for example, is regarded by the poor and ignorant under the form of a very fortunate person, able to purchase luxuries which are above their own reach; by the religious mind under the form of a person with: more than ordinary temptations to contend with; by the political economist under that of an example of the unequal distribution of wealth; by the tradesman under that of one whose patronage is valuable. Now the object is really the. same to all these observers; the sauce rich man has been represented under all these different forms. And the reason that the observers are able to find many in one is that they connect him severally with their own prior conceptions. The form, then, in this view, is mode of knowing, and the matter is the perception or object we have to know" (Thomson, Outline of Laws of Thought, page 34). Sir W. Hamilton calls the theory of substantial forms "the theory of qualities viewed as entities conjoined with, and not as mere dispositions or modifications of matter" (Hamilton's edition of Reid's Works, page 827).
Dr. M'Cosh remarks, on the distinction between form and matter, that "this phraseology was introduced by Aristotle, who represented everything as having in itself both matter (ὕλη) and form (εϊvδος). It had a new signification given to, it by Kant, who supposes that the mind supplies from its own furniture a form to impose on the matter presented from without. The form thus corresponds to the a priori element, and the matter to the a posteriori. But the view thus given of the relation in which the knowing mind stands to the known object is altogether a mistaken one. It supposes. that the mind in cognition adds an element from its own resources, whereas it is simply so constituted as to know what is in the object. This doctrine needs only to be carried out consequentially to sap the foundations of all knowledge; for if thee mind may contribute from its own stores one element, why not another? whey not all the elements? In fact, Kant did, by this distinction, open the way to all those later speculations which represent the whole universe of being as an ideal construction. There can, I think, be no impropriety in speaking of the original principles of the mind as forms or rules, but they are forms merely, as are the rules of grammar, which do not add anything to correct speaking and writing, but are merely the expression of the laws which they follow. As to the word matter,' it has either no meaning in such an application, or a meaning of a misleading character" (Intuitions of the Mind, N.Y. 1866, page 308). Formal, in philosophy, is that which relates to the form, as opposed to material, or that which relates to the matter. So formal logic gives the theory of reasoning as grounded in the laws. of thought, without reference to the subject-matter to which reasoning may be applied. — Fleming, Vocabulary of Philosophy, s.v.; Krug, Handwort. der philosoph. Wissenschaften, 2:56.