 Now, in logic theories are treated as sets of sentences and the objects (if any) that sentences talk about appear as elements of the domain of set-theoretic entities called structures. Associated with these structures are interpretation functions that map individual constants onto individual objects of the domain and n-place predicates onto n-tuples of elements in the domain. When a structure makes all the sentences of a given theory true it is called a model of the theory. By demonstrating that there is a model of T we show theory T is consistent. If T turns out to be true in its intended model, then T is true simpliciter. 