The grammar of Classical Nahuatl is agglutinative, head-marking, and makes extensive use of compounding, noun incorporation and derivation. That is, it can add many different prefixes and suffixes to a root until very long words are formed. Very long verbal forms or nouns created by incorporation, and accumulation of prefixes are common in literary works. New words can thus be easily created. Orthography used in this article Vowel length was phonologically distinctive in Classical Nahuatl, but vowel length was rarely transcribed in manuscripts, leading to occasional difficulties in discerning whether a given vowel was long or short. In this article, long vowels are indicated with a macron above the vowel letter: <ā, ē, ī, ō>. Another feature which is rarely marked in manuscripts is the saltillo or glottal stop ([ʔ]). In this article, the saltillo is indicated with an h following a vowel. The grammarian Horacio Carochi (1645) represented saltillo by marking diacritics on the preceding vowel: grave accent on nonfinal vowels <à, ì, è, ò> and circumflex on final vowels <â, î, ê, ô>. Carochi is almost alone among colonial-era grammarians in consistently representing both saltillo and vowel length in transcription, even though they are both essential to a proper understanding of Classical Nahuatl. Morphophonology The phonological shapes of Nahuatl morphemes may be altered in particular contexts, depending on the shape of the adjacent morphemes or their position in the word. Assimilation Where a morpheme ending in a consonant is followed by a morpheme beginning in a consonant, one of the two consonants often undergoes assimilation, adopting features of the other consonant. Almost all doubled consonants in Nahuatl are produced by the assimilation of two different consonants from different morphemes. Doubled consonants within a single morpheme are rare, a notable example being the verb -itta "see", and possibly indicates a fossilized double morpheme. Morphology The words of Nahuatl can be divided into three basic functional classes: verbs, nouns and particles. Adjectives exist, but they generally behave like nouns and there are very few adjectives that are not derived from either verbal or nominal roots. The few adverbs that can be said to exist fall into the class of particles. Nouns Classical Nahuatl is a non-copulative language, meaning it lacks a verb meaning 'to be.' Instead, this meaning is conveyed by simply inflecting a noun as a verb. In other words from the perspective of an English speaker, one can