To understand the difference betweenthematic and functional categories we first need to introduce concepts to do with how the elements of a sentence can be related to each other. Take a simple sentence:

(33)Peter chased Mary

This sentence describes an event which can be described as ‘chasing’ involving two individuals, Peter and Mary, related in a particular way. Specifically, Peter is the one doing the chasing and Mary is the one getting chased. The verb describes the character of the event and the two nouns refer to the participants in it. A word which functions as the verb does here, we call apredicate and words which function as the nouns do are called arguments. Here are some other predicates and arguments:

(34)a  Selena      sleptargument predicateb    Tom       is tallargument predicatec   Percy       placed     the penguin    on the podiumargument  predicate      argument       argument

In (34a) we have a ‘sleeping’ event referred to involving one person, Selena, who was doing the sleeping. In (34b) the predicate describes a state of affairs, that of ‘being tall’ and again there is one argument involved, Tom, of whom the state is said to hold. Finally, in (34c) there is a ‘placing’ event described, involving three things: someone doing the placing,Percy, something that gets placed, the penguin, and a place where it gets placed,on the podium.