Modern Greek now uses only one accent, the acute accent (η οξεία), to indicate the stressed syllable on words with more than one syllable (it is only used with some one-syllable words to distinguish them from other words spelled the same way). Previously, for historical reasons, Greek used three accents (acute, οξεία; grave, βαρεία; and circumflex, περισπωμένη) and two breathings (rough breathing, δασεία; smooth breathing, ψιλή).
Since all three accents had the same function in modern Greek (to indicate the stressed syllable) and did not make any difference in sound, and the breathings were not pronounced at all, the Greek government decided on 1 September 1982 to introduce the present, simplified system with only one accent and no breathings. However, you will probably come across books written in the old system, and many old people who are used to the old system still write that way (as do Elder Saxey and Elder Newton). The Book of Mormon and Doctrine and Covenants/Pearl of Great Price in Greek are printed using the polytonic system (without the grave accent, however, which they replace by the acute accent). The Greek Orthodox Church also still likes to use the polytonic system, especially when they write in καθαρεύουσα.
Here is an example text in both monotonic and polytonic, so you can see the difference (it's Doctrine and Covenants 4:4):
"Full" polytonic (with grave accent):
Monotonic:
When you are reading a text written in polytonic, just remember that the breathings
and
are not
pronounced, and that all three accents
,
, and
simply indicate the stressed syllable. Accents sometimes occur on the same letter with
breathings; in this case, ignore the breathing and just "pronounce" the
accent.