Maybe it's absurd to include all relational properties in the nature of a thing. Some belong there, others do not. A boy has an I.Q. of 120. He also wears Arrow shirts. It will be said that the I.Q. characteristic is genuinely essential to him, since his intellectual superiority in certain respects to others of his age could not be removed without a significant difference in his own nature.
But there's nothing essential in his wearing a certain brand of shirts, since he could wear another brand while remaining the person he is. Even though both properties belong to his nature, the first belongs essentially, and the brand of shirts he wears belongs to his nature only accidentally or by chance. Consequently, there are internal and external properties, just as there are internal and external relations.
That could mean that a sharp line can be drawn between the alleged classes of internal and external properties. But this has already been rejected (18.104.22.168-22.214.171.124) The problem of demarcating essences is notoriously insoluble. If the term is an individual, the characteristics that make up its nature are inexhaustible. That's why an individual is not logically definable. An individual has an unlimited number of differientiating characteristics. If the term is general, then trying to state the essence, either that some constant characters have been taken for granted and left out, or that some constant characters have been taken as the essence for irrelevant reasons, such as serving most conveniently to set a figure before us, or that essence and properties (in the logical sense) are interchangeable, or, as in the case of organic kinds, that different characters have differing importance in the determination of other characters, suggesting that essentiality is a matter of degree.
So also of accidents. It's impossible to marke them off sharply from either essence or property. What is blackness to the crow? Is it a separable accident, an inseparable accident (whatever that means), a property , or part of what crows are essentially? Any answer to this question would be wrong.
Crow nature is an immensely complicated thing, and blackness may be intimately connected with many features of it, themselves of varying importance and connected with varying degrees of intimacy. In all probability, the color is neither a mere accident, nor yet as indispensable a part of crow nature as certain other attributes. The color lies in what is logically a no-man's land between pure accident and pure necessity.
These old sharp lines of mutual exclusion between essence, property, and accident are like the lines of a surveyor. Of great coconvenience, no doubt, to ourselves, but misleading when taken as divisions marked out by nature.
The other meaning of the distinction would admit that the division between internal and external characteristics is one of degree only. Thus the characteristic of being intellectually in advance of others of one's age would be a relatively essential one, and the characteristic of being the wearer of a certain brand of shirt is a relatively unessential one, since the difference in the boy's nature involved in the absence of the I.Q. characteristic would be far more pervasive than that involved in the absence of the Arrow shirt.
To call the I.Q. characteristic internal absolutely would be a mistake, since the removal of that characteristic would not leave the subject simply and totally oehter than the boy was, but only particlaly so. And the Arrow shirt characteristic is not absolutely external either. Being the wearer of one kind of shirt rather than another is a trivial characteristic of anyone. But we are dealing, not with the prepared abstractions of logic books, but with attributes in their concrete setting. This characteristic reveals the wearer's choice, and thus is bound up in intimate fashion with his standards of taste, his proneness to imitate, his openness to suggestion, and is therefore in its absence he would be exactly the same.
To the believer in degrees, such an assertion would be ill-judged. It ouwld be hardking back to the view that persons or minds are mosaics. But hard as it may be to say what the other characters are with which the Arrow-shirt-wearing is connected, or precisely how it is linked to them, the relation is not that of one marble to others in a box, this trait could not be difference unless the wearer's choice had been different, and his choice could not have been different without his being different.
The characteristic may not be an important part of his nature, but it is a part nevertheless. It's not merely external. It is internal, even though internal only in degree. ('Make a difference in' is used ambiguously to mean both 'logically determine' and 'causally determine'. This does not matter, since causal determination always contains an element of logical necessary. (126.96.36.199ff)
But notice that this view is merely a refinement of the internal relations theory. It is a reply to the argument that all of a thing's relations give rise to properties, and that these properties belong to its nature. The reply was that even if that is true, they do not belong to its nature equally. Some are irrelevant, some are essential. But what this really means is that their removal would involve the alteration of the thing in very different degrees. And this is the internal relations theory about internal characteristics.