Vagrant predicates are logical constructions that exhibit an inherent limit to conceptual knowledge. Such predicates can be used in general descriptions but are self-contradictory when applied to particulars. For instance, there are numbers which have never been mentioned but no example can be given as this would contradict its definition. Vagrant predicates have been proposed and studied by Nicholas Rescher

Nicholas Rescher

Nicholas Rescher is an American philosopher at the University of Pittsburgh. In a productive research career extending over six decades, Rescher has established himself as a systematic philosopher of the old style and author of a system of pragmatic idealism which weaves together threads of...

.

F is a vagrant predicate iff

IFF

IFF, Iff or iff may refer to:Technology/Science:* Identification friend or foe, an electronic radio-based identification system using transponders...

 (u)Fu is true while nevertheless Fu₀ is false for each and every specifically identified u₀.

When infinity

Infinity

Infinity is a concept in many fields, most predominantly mathematics and physics, that refers to a quantity without bound or end. People have developed various ideas throughout history about the nature of infinity...

 is thought as number greater than any given, a similar idea is conceived. However vagrancy needs not to be monotonous and occurs also within bounds. Rescher has used vagrant predicates to solve the vagueness

Vagueness

The term vagueness denotes a property of concepts . A concept is vague:* if the concept's extension is unclear;* if there are objects which one cannot say with certainty whether belong to a group of objects which are identified with this concept or which exhibit characteristics that have this...

problem.