Enclitics are words that do not have any stress and are phonologically dependent on their preceding word. In English, definite and indefinite articles (the, a, an) are examples for an enclitic.
Persian's indefinite article is also an enclitic. Enclitics form part of the syllable of their host word and change its normal syllable structure (syllabification). For example, in "pedar" (father), the syllabification is pe-DAR, but in "pedar i" (a father), the syllabification becomes pe-DA-ri. That is, it become a three-syllable word with the stress on the penultimate syllable. Compare the enclitic "i" with the suffix "i" in "pedari" (paternal), where the syllabification is pe-da-RI: a three-syllable word with the stress on the last syllable, as is regular in Persian.
Although phonologically dependent, enclitics have a distinct grammatical role and are syntactically independent from their preceding word. Therefore, they should be written separately. Languages like English and French, write their enclitics separately. In Middle Persian, enclitics were written as separate words as well but in New Persian, the majority of enclitics are written attached to their host word. As a result, "pedar i" (a father) and "pedari" (paternal) are written identically as پدری.
For educational purposes, the following enclitics are separated from their host word with a hyphen: