What is another word for because I said so?
Pronunciation: [bɪkˈʌz a͡ɪ sˈɛd sˈə͡ʊ] (IPA) 
The phrase "because I said so" is often used as a dismissive response to questioning or logic, but there are plenty of alternative expressions that can be used instead. One is "there's a good reason for it," which implies that there is a logical explanation rather than just an authoritarian decree. Another option is "it's important for X reason," where X is the relevant factor that makes the decision necessary. Or, simply explaining the rationale behind a decision can avoid the need for any dismissive phrase - instead, people will understand why you're making a particular choice and be more likely to cooperate.
