The former is caused by word-accent, the latter by the rhetorical accent, as illustrated by the last examples.
Sometimes verse-accent and word-accent do not correspond even at the last accent in a colon.
The main law for all accentual versification is this, that verse-accent must always coincide with word-accent.
In both cases the rhythmic accent has to yield to the word-accent.
The incidence of word-accent is left unfixed save so far as the incidence of verse-accent enables us to fix it.