Hi Shirley Regarding your 1st question, it is recommended not to substitute ئ with ی as they are different letters and they sound differently. This substitution is a common mistake as they look similar and the former character has been directly borrowed from Arabic. Therefor, it is رئیس and not the other way around. And with respect to your 2nd question, the short answer is yes you can. However, it sounds more natural and native-like to use their Arabic counterparts. At least, for the aforementioned words. Thus, دلیل ها as well as منبع ها and ساحل ها is acceptable. Best Ehsan

My recommendation about the second question: In case you are not sure what is the correct irregular form and you do not have enough time to check it (for example in a speaking situation), simply add ها. Even though it does not sound natural, it is not wrong. But as a long term goal, do not ignore irregular forms and try to use and memorize them, specially in your writings. Because irregular forms are more formal and sound much more natural

hi , first excuse me if my english is not very well about your second question in farsi we just have 1 ان and 2 ها for making the persian word plural in persian speaking nowdays we use ها for almost all words,and yes you can use ها for all cases as you uknow three is a a alot of arabic word in persian unfortunately and in arabic you can make word prulal in 5 way like word + ون word +ین word +ات and in farsi we sometime for abaic words we use arabic plural form of them but we can also use arabic words with ان and ها for example معلم means teacher is a arabic word but we say معلم ها for plural form or another example قاعده is arabic and its plural form is قواعد and its commen in iran to use it but you can also day قاعده ها and thats fine at the end in 99 percent of cases is speaking there is no problem to use ها for persian words even arabic word and persian listener can underastnd what is your mean about second question its hard question id have enough information to answer it :( buts its also related to to arabic words in persian :/

Dear my friend, answering your first question I should say in standard Persian you can just use دایم and دائم nowadays is considered as an Arabic word .However, some times people use دائم for دایم.So you`d better use دایم