R. Whitney Tucker (1965), "Accentuation before Enclitics in Latin", Transactions and Proceedings of the American Philological Association, 96: 449-461 wrote:We must also remember that in Latin enclitics are of several different types, and that it is at least theoretically possible that these were treated differently with respect to accentuation. They may be listed as follows:
1. Inseparable enclitics, those which exist only in connection with a limited number of base-words, with no independent meaning of their own, where the resulting combination has a new and different meaning. The base-word and the enclitic may be said to have coalesced into a new word. Examples are -dam as in quidam, -dem as in Idem or quidem, -que (generalizing) as in quisque, -quis, etc. as in quisquis, -piam as in quispiam, and -cumque as in quicumque or ubicumque.
2. Separable, or movable, or optional enclitics, which may be attached at will to certain words, or to any word, when their specific meaning needs to be added. These are -que 'and,' -ve, -ne, -ce, -met and -te (as in tute), -pse and -pte, -nam, -dum. The first four of these are the classic examples usually cited by the ancient grammarians.
3. Normal words which may sometimes be used as enclitics; these are often difficult to identify, but still there are many cases where their enclitic character is unmistakable. Examples: various forms of esse and fieri, especially in the present tense; the personal and reflexive pronouns, and sometimes the demonstratives; cum; quis (as in siquis) ; per in parumper; inde as in deinde and proinde. (pp.450-1)