Nouns ending in a consonant followed by -y change the -y to -ies in the plural form.
Authority is regular. It follows the -ies Conversion rule.
Use plural verbs: "The authorities are ready" (not "is ready").
Yes. The plural authorities is standard across all English variants.
The word authority follows the standard English pluralization rule. When forming the plural, authority becomes authorities. This follows the -ies Conversion pattern, which is one of the most common plural rules in English.
Understanding why authority becomes authorities helps with spelling and pronunciation. Nouns ending in a consonant followed by -y change the -y to -ies in the plural form.
When using authorities in writing, remember that it functions as a plural noun in sentences. It pairs with plural verbs and pronouns. For example: "The authorities are ready" (not "is ready"). This subject-verb agreement is essential for grammatical correctness.