The ي as Augmentative Letter
The ي can be judged to be augmentative in following cases:
When the ي is accompanied by 3 or more root letters. There can be other augmentative letters in the word in addition to ي
فِعِّيل - صِدِّيق - ص د ق
فِعِّيلَة - صِدِّيقَة - ص د ق
فَعْلَانِيّ - نَصْرَانِيّ - ن ص ر
فَعْلَانِيَّة - رَهْبَانِيَّة - ر ه ب
فِعْلِين - غِسْلِين - غ س ل
فِعْلِيَآء - كِبْرِيَآء - ك ب ر
فِعْلِيت - عِفْرِيت - ع ف ر
يَفْعُول - يَنْبُوع - ن ب ع
يَفْعِيل - يَقْطِين - ق ط ن
إِفْعِيل - إِدْرِيس - د ر س
إِفْعِيل - إِبْلِيس - ب ل س
فَعِيل - نَذِير - ن ذ ر
فَعِيل - شَهِيد - ش ه د
فَعِيلَة - خَلِيفَة - خ ل ف
فُعَيْل - رُوَيْد - ر و د
فِنْعِيل - خِنْزِير - خ ز ر
فِعْمِيل - قِطْمِير - ق ط ر
فَعْلَلِيل - زَنْجَبِيل - ز ن ج ب ل
فَعْلَلِيل - سَلْسَبِيل - س ل س ب ل
فَمْعَلِيل - زَمْهَرِير - ز ه ر
يَفْعَلُ - يَجْهَلُ - ج ه ل
يُفَعَّلُ - يُبَصَّرُ - ب ص ر
يُفَاعِلُ - يُحَافِظُ - ح ف ظ
يُفْعِلُ - يُقْصِرُ - ق ص ر
يَتَفَعَّلُ - يَتَدَبَّرُ - د ب ر
يَتَفَاعَلُ - يَتَعَارَفُ - ع ر ف
يَسْتَفْعِلُ - يَسْتَقْدِمُ - ق د م
مُفَيْعِل - مُصَيْطِر - س ط ر
Notes:
1. In last example above, root is written with س while in word ص is written. This is substitution of ص for س . InshaALLAH more will be discussed in series on substitution.
2. in reduplicated roots in which a 2 letter root is repeated to make a 4 letter root, the ي is not augmentative.
فُعْفُع (فُعْلُل) - يُؤْيُؤ - ي أ ي أ
3. With only 2 other root letters, it is also root letter and not an augmentative letter.
فَعْل - بَيْت - ب ي ت
4. If the ي is accompanied by 2 root letters and a أ or م as 1st letter then usually that أ or م is judged to be augmentative while the ي is judged to be root letter.