text: sentence would be true or false. One of its central methodological 
  assumptions is the principle of compositionality. It states that the 
  meaning of a complex expression is determined by the meanings 
  of its parts and how they are combined. For example, the meaning 
  of the verb phrase "walk and sing" depends on the meanings of the 
  individual expressions "walk" and "sing". Many theories in formal 
  semantics rely on model theory. This means that they employ set 
  theory to construct a model and then interpret the meanings of 
  expression in relation to the elements in this model. For example, 
  the term "walk" may be interpreted as the set of all individuals in 
  the model that share the property of walking. Early influential 
  theorists in this field were Richard Montague and Barbara Partee, 
  who focused their analysis on the English language.[173] 