【正确答案】Speech act is a basic unit of communication that includes perlocutionary，illocutionary，and locutionary Speech act is a communicative activity，defined with reference to the intentions of the speaker while speaking and effects he achieves on his hearer．This speech act theory was originated with the British philosopher John Austin in the late 50’s of the 20th century．According to him，a speaker might be performing three acts simultaneously when speaking: locutionary act，illocutionary act，and perlocutionary act．