@Zetherin,
Zetherin;113933 wrote:...
What sort of thing, if any, do you think Russell would call a "convenient non-fiction", or just a "non-fiction"?
...
I would imagine that he would think of the chair upon which he sat as a convenient non-fiction. A non-fiction would be an actual object, like a table, chair, tree, or person. And "convenient fictions" would be useful concepts that do not have physical instantiations. However, this is me guessing rather than finding anything in Russell regarding your question.