caleteu wrote:I am confused. Is there a rule for the addition or substraction of א ?
The plural of ברייה for example, is בריאות
The passive participle of מילא for example isמילוי
I know that the root of both words ends on א . Is there a rule for the addition or substraction of א?
First of all, aleph and heh are very unstable consonants, which are prone to either lose their consonantal values and remain as purely orthographic fossils, or they may drop out entirely. This is something you might discover only if you dwelve into the older layers of Hebrew. In Modern Hebrew usually only one form of a word is accepted so it can be confusing.
Unlike the letter ע, aleph is a rather inaudible gluttural sound and it loses it's consonantal value whenever you'll find it at the end of the word. It merely signals the preceeding long vowel (for the sake of argument; in Modern Hebrew there is no difference between long and short vowel) ====)
מִלּוּא (it's a doublet, the same meaning as מילוי), מָלֵא , הֵבִיא, חֵטְא (חָטָא) , שְׁוָא etc. Aleph is completely silent, merely orthographic.
(In cases like דוגמא, קופסא etc, the aleph is a remnant of the Aramaic definite article. So קופסא in Aramaic is basically הקופסה in Hebrew. You may find in Hebrew both forms קופסא and קופסה, but language purists would insist on קופסה.)
Usually when a word or syllable begins with aleph, it retains it's consonantal value. However, there are words when even in such cases the aleph is violently supressed (it is made silent) and remains in the word purely as an embelishment. ====)
מְלָאכָה, מְלַאכְתֶּךָ, יִשְׁמָעֵאל , (future tense of verbs that begin with aleph like אכל - אוכל)
And so it happens, that in cases when aleph looses its consonantal value it might be substituted with י or ה. Like ימלא can be also ימלה and ראם can be also רים and מילוא can be also מילוי and so ברייה is the same as בריאה and so on.
In many instances it's just dropped ====)
יצאתי - יצתי
מלאתי - מלתי
חמאה - חמה
And many more... these are all doublets and show how unstable aleph was and in spoken biblical language it seemingly didn't play significance, as it was often dropped by the scribes themselves. In Modern Hebrew, in these cases, only the forms with aleph exist.
There are many more rules as to what happens to these weak letters and when these changes occur, but if you're not interested in the very deep linguistic understanding of Hebrew, I think it's irrelevant. In case you find this interesting I recommend to start with Gesenius grammar book.
What exactly is the difference between סירה and אונייה?