Elaboration
In my judgment and by my definition, inseparable attributes can't exist separately from the existents of which they are attributes. Even so, they can be separated mentally in the imagination by means of a process of abstraction.
For example, mentally, it's possible for me to imaginatively separate its attribute of length from a blade of grass. In reality, though, the blade and its length can't be separated.
Treating such an abstracted attribute, or any inseparable part of a whole, as if it could exist separately in reality, by my definition involves the fallacy of reification.
(Please note: since concept-formation involves a process of abstraction, sometimes the term "abstraction" is also used as a synonym for the term "concept." I use the term "abstraction" to denote a process, though, which itself is part of the process of concept-formation - and I use the term "concept" to denote an eventual product of that process of which abstraction is a part.)
Note
1Although I've formulated this definition in my own words, in my judgment, I drew inspiration and benefit in doing so from Ayn Rand's discussion of abstraction in her book, Introduction to Objectivist Epistemology.
