Prisican on the Stress of calefacit.

On pg. 127 fn. 16 I mention that calēfacit was probably accented as if two words, i.e. cálē fácit, which allowed the ē to undergo Iambic Shortening.  In support of this I note the failure of the a of facit to weaken and the occasional inversion and/or separation of the two parts. In addition I should have mentioned the explicit testimony of Priscian (Keil 2:402):

si uero facio uerbo uel fio integris manentibus aliud uerbum infinitum ante ea componatur, non solum significationes et coniugationes integras eis seruamus, sed etiam accentus, ut calefácio calefácis calefácit, tepefácio tepefácis tepefácit. in secunda enim et tertia persona paenultimas acuimus, quamuis sunt breues. similiter calefio calefís calefít, tepefio tepefís tepefít finales seruant accentus |in secunda et tertia persona, quos habent in simplicibus. 

If another non-finite verb form is compounded with facio or fio, which remain unweakened, these verbs retain not only their meaning and conjugation type, but also their stresses, e.g. calefácio calefácis calefácit, tepefácio tepefácis tapefácit.  In the 2nd and 3rd person we stress the penult although they are short.  Similarly, calefio calefís calefít, tepefio tepefís tepefít  preserve in the 2nd and 3rd person the oxytone accent that they have in the simplex.

The Grammarians on Latin Stress

On pg. 110 I give a few simple statements about calculating the position of the word stress in Latin and in fn. 21 I quote a Cicero passage (Orat. 58) which is normally taken as explicit testimony for the antepenult limitation—although it should be noted that it is not entirely clear that Cicero is talking specifically about Latin, the context could suggest a reference to Greek. I should also have quoted statements of other native speakers supporting the other parts of the system.

Quintilian (Inst. 12.10.33) notes that there are (with a few exceptions) no oxytones in Latin:

ultima syllaba nec acuta umquam excitatur nec flexa circumducitur.

"The last syllable is never accented either as an acute or a circumflex."

Donatus (Keil 4.371) remarks that in bisyllabic words the penult is stressed no matter whether it is short or long (the description is complicated by the grammarian's theory that long vowels in the penult could be either circumflex or acute as in Greek):

in disyllabis, quae priorem productam habuerint et posteriorem correptam, priorem |syllabam circumflectemus, ut meta, Creta; ubi posterior syllaba producta fuerit, acuemus |priorem, siue illa correpta fuerit siue producta, ut nepos, leges; ubi ambae breues fuerint, |acuemus priorem, ut bonus, malus.

"In bisyllables which have a long first syllable and a short final syllable we give the first syllable a circumflex, as in mêta and Crêta; When the second syllable is long, we give the first syllable an acute, whether it is short or long, as in népōs and l'ēgēs; when both syllables are short we give the first an acute as in bónus and málus."

Donatus also provides explicit testimony about the importance of the weight of the penult (Keil 4.371):

In trisyllabis et tetrasyllabis et deinceps, si paenultima correpta fuerit, acuemus |antepaenultimam, ut Tullius Hostilius; si paenultima positione longa fuerit, ipsa acuetur |et antepaenultima graui accentu pronuntiabitur.

"In three- and four-syllables and so on, if the penult is short we the give the antepenult an acute, as in Túllius and Hostílius; if the penult is long by position, it gets an acute and the antepenult not accented."