historically, generative proposals made focus a feature bound to a single word within a sentence. chomsky and halle formulated a nuclear stress rule that proposed there to be a relation between the main stress of a sentence and a single constituent. since this constituent is prominent sententially in a way that can contrast with lexical stress, this was originally referred to as "nuclear" stress. the purpose of this rule was to capture the intuition that within each sentence, there is one word in particular that is accented more prominently due to its importance – this is said to form the nucleus of that sentence.