There is a final
rule that often circumvents the need for memorizing vowel quantities:
A vowel is considered long by
position when directly followed by two consonants, whether in the
same word or beginning the subsequent word.
instance, if the nominative nauta immediately precedes the verb scit,
the final -a becomes long for the purpose of filling out the meter: nautâ
scit. (The word is still nominative, of course.)
rule is not ironclad, as certain consonant combinationsólike -cr, -pr, and -trówill
not always "make position."
consonant -h- is not usually considered a full consonant, and will not cause a
vowel to make position.
For instance, in the phrase tenet haec ("she understands these things"),
the syllable -et in tenet is short, not long.
consonants -x- and -z- make position
all by themselves, since they are actually double consonants (-ks- and -ds-, respectively).
combination -qu-, which is pronounced -kw-, just as in English, is treated as
a single consonant, and never makes position.
Furthermore, the -u- never receives a long or short mark during scansion,
as is the practice for consonants.
vowel -i- is sometimes considered a consonant, usually when it begins a word and
is followed by a vowel. In such cases, e.g. Iuno, the -i- is pronounced
as an English -y- (which, recall, is likewise sometimes a vowel, sometimes a consonant).
rule of thumb is to find a derivative from the word in question: if the -i- becomes
a -j- in English (e.g. Juno > Iuno), then it is a consonant, and may help another
word make position.
Furthermore, the -i- in question should not receive a long or a short mark.