If it is in the dual form or a masculine sound plural it is...

If it is in the dual form or a masculine sound plural it is made indeclinable on a yā' , for example: لا عالِمَینِ و لا عالِمِینَ في المدینة. If the compound number is inbetween 11 and 19, excluding 12, both of its parts are made indeclinable on a fathah , for example: جاءنی خمسَةَ عَشَرَ رَجُلاً.

The six directions, which are:، تحتُ ، یمینُ ، شمالُ ، خلفُ و قُدَّامُ فوقُ and whatever else has their meanings, for example: قَبلُ ، بَعدُ ، أولُ ، دونُ ، و حسبُ, are all made indeclinable on a dummah . Verbs that are necessarily indeclinable are the preterite tense and the imperative. The preterite tense is made indeclinable on a fathah .

Hence, it is correct to say that if a plural wāw or nominative pronoun is added to it, it would have an implied fathah due to the vowel sign in congruence with the wāw in the first case and the sakūn in the second. An imperative is made indeclinable on a sakūn if the feminine nūn is added to it, for example: اِحفَظنَ or its last letter is sound and there is nothing added to it, for example: اِحفَظ.

Indeclinable signs are implied just like declinable signs are, either because another sign takes its place or because there is a reason that it cannot be mentioned, for example in vocatives, whether they be indeclinable before the vocation (ی ا حِذامِ) or declinable before it (یا یحییَ), or in aorist tense verbs ending in an alif ( دَعا) , or the subject of a lā that denies a whole genius ( لا فتیَ هُنا). Previous…