the following example. Word order variation Zapotec languages also show the phenomenon known as pied-piping with inversion, which may change the head-initial order of phrases such as NP, PP, and QP. Verbal morphology Passive morphology A few varieties of Zapotec have passive morphology, shown by a prefix on the verb. Compare Texmelucan Zapotec root /o/ 'eat' and its passive stem /dug-o/ 'be eaten', with the prefix /dug-/. In many other cases, the transitive-intransitive verb pairs are appropriately described as causative vs. noncausative verb pairs and not as transitive-passive pairs. Causative morphology Most if not all varieties of Zapotec languages have intransitive-transitive verb pairs which may be analyzed as noncausative vs. causative. The derivation may be obvious or not depending on the kinds of sounds that are involved. In the simplest cases, causative is transparently seen to be a prefix, cognate with /s-/ or with /k-/, but it may also require the use of a thematic vowel /u/, as in the following examples from Mitla Zapotec: Setting aside possible abstract analyses of these facts (which posit an underlying prefix /k-/ that causes the changes seen superficially), we can illustrate the kinds of non-causative vs. causative pairs with the following examples. (Basic intransitive verbs are more common than basic transitive verbs, as in many languages.) The presence of the theme vowel /u-/ should be noted in the causative verbs, and in some cases is the only difference between the two verbs. One example of a double causative is also included here; these are not possible in all varieties. Aspectual inflection Verbs in Zapotec languages inflect with prefixes to show grammatical aspect. The three aspects that are found in all varieties are habitual, potential and completive. San Lucas Quiaviní Zapotec has seven aspects: habitual, perfective, irrealis (viz., potential), progressive, definite (viz., completive), subjunctive, and neutral. The shape of the root affects the way in which verbs conjugate. Consonant-initial roots conjugate differently than vowel-initial roots, for example, and causative verbs conjugate differently than simple verbs. Prefix vowels may be lost or merged with the root vowel, epenthetic vowels and consonants may be found, and root vowels may be affected. The following example shows the aspectual inflection of three verbs in Mitla Zapotec. Noun morphology There is virtually no true morphology in the Zapotec noun. There is no case marking. Plurality is indicated (if at all) in the noun phrase, either by a number or