Weak forms are reduced pronunciations of small grammatical words in English like articles, prepositions, and auxiliary verbs. These words are pronounced with schwa or short 'i' vowel sounds in unstressed positions but take on a full pronunciation, or strong form, when stressed or at the end of a sentence. Native English speakers rely heavily on weak forms in fluent speech. Learners must become familiar with weak forms to accurately understand native speakers and to speak English fluently themselves, as overusing strong forms results in unnatural, foreign-sounding pronunciation.