Any definition of human language, regardless of one’s theoretical affiliation, includes some mention of the mandatory hierarchical LEVELS of language, beginning with the smallest units of language and ending with the largest possible units. Most definitions of human language state that the smallest unit of language is the phoneme, which is the minimum distinctive unit of speech sound, a bundle of distinctive features (e.g. voicing, vocalic, nasality, consonantal, etc.). Because human language is generally learned through the aural medium initially, preference in definitions of language is given to speech sound. However, it is also acknowledged that the minimum distinctive unit of written language is the grapheme.