Most humans hear an inner voice when thinking or reading. Some people completely lack inner speech. Inner speech links to subtle throat movements like overt speech. Gilbert Ryle deemed it central to self-knowledge. Vygotsky observed it develops from children's overt private speech. Inner speech sharpens thoughts like external talk or writing. It enables analyzing daily situations like timing dinner versus watching a match. Inner speech often occurs unintentionally and resists suppression. Suppressing it intensifies it paradoxically. Stress, anxiety, and depression tie to excessive inner speech. Generating inner speech requires no conscious effort unlike overt speech. It forms a unique conscious experience mimicking external talking internally. Philosophy only recently fixated on inner speech despite psychology's prior interest. Further study may reveal if it's personality trait or evolutionary byproduct of intelligence.