What is Non-Logical Vocabulary

Question

Non-Logical Vocabulary: 1. Predicates, called also relation symbols, each with its associated arity. For our
needs, we may assume that the number of predicates is finite. But this is not essential. We can have an infinite list of predicates, P₁, …, P_n, …, provided that the arity of P_n can be effectively computed as a function of n. 
         
2. Individual constants, c₁, c₂,… We shall assume that their number is finite, but this again is not essential.

3. Function symbols, f₁, f₂, … each with its associated arity. Again, we may assume that their number is finite, but this is not essential as long as the arity of f_n is a computable function of n.