Which syllable gets the stress

I know the general principles governing which syllable gets the stress.. There are exceptions, and often there are guidelines which help you out. However, with the words accomodare, accomodati, and accomodatevi I'm not sure why the stress falls where it does.  I will capitalize the syllables that are stressed (or where I believe the stress is placed):

ac-co-mo-DA-re/ac-co-mo-DAR-si

ac-CO-mo-da-ti

ac-co-mo-DA-te-vi

The first and third words follow the guidelines I know-so no problem there

Unless I am wrong, the second word has the stress placed as noted (ac-CO-mo-da-ti). Assuming I'm correct about the stressed syllable, can someone (please) let me know why the 3rd from the last syllable is stressed in this case and not the 2nd from the last syllable as with divertiti (di-VER-ti-ti). Thanks in advance for the help. 

PS: I will be embarrassed if I'm wrong about the location of the stressed syllables, but learning a foreign language is fun but not always easy

Hi JS, 

Thanks for your question!

Italian syllables are not as straight-forward so I do understand the challenge in this case.

By looking at the first-person singular form of an Italian verb you would generally be able to understand the pronunciation pattern for that verb in the simple present indicative. The first-person pronunciation, or really where to put the stress, applies to the singular forms and the third-person plural form. The first-person and second-person plural forms have a more predictable pronunciation.

For instance, let's take ac-co-mo-DA-re:

io ac-CO-mo-do
tu ac-CO-mo-di
lui/lei ac-CO-mo-da
noi ac-co-mo-DIA-mo
voi ac-co-mo-DA-te
loro ac-CO-mo-da-no

You can see that io, tu, lui/lei and loro share the same stress while noi and voi have the stress in the ending.

Certain Italian verbs, usually those with Latin roots, are accented differently from the norm. Instead of the stress falling on the usual next-to-last syllable, the stress falls on the third-to-last syllable.

This is usually referred to as “Retrocessione dell’accento” for which identifying the stressed syllable in the conjugation of a verb can be tricky. 

I invite you to check out this list to see a series of examples of verbs that have a different stressed syllable for “io”, “tu”, “lui/lei” and “loro”.

Hope this helps! :)