In English, some predicates have optional arguments.
Claire gave
Claire gave Scruffy
Claire gave Scruffy to Mike
In FOL, the number of arguments a given predicate can take is fixed. Its called the "arity" of the predicate.
In English, predicates are sometimes vague.
FOL assumes that to every predicate their corresponds a determinate property or relation, i.e. one for which given any object or set of objects, there is a definite fact of the matter whether or not the objects have that property or are in that relation.