Learn Farsi: همه‌ی همسایه‌ها به مراسم می‌آیند.

همه means all. To connect it to the noun it describes, we use the linking sound called ezāfe. Because همه ends in a vowel sound, the ezāfe is written with the letter ی (ye), making it همه‌ی (hame-ye).

Why is the noun همسایه‌ها plural here? Could I just say همه همسایه?

When you use همه to mean all of a specific group of countable things, the noun that follows must be plural. So we have to use همسایه‌ها (neighbors) with the plural suffix ها, rather than the singular همسایه.

The word for neighbor, همسایه, ends in the letter ه. How does the plural suffix ها attach to it?

When a word ends in the short e sound written with ه, you simply place the plural suffix ها right after it. In Farsi script, these two letters do not physically connect, which is why it looks like همسایه‌ها.

Why does the verb می‌آیند have that hat symbol over the alef?

The verb to come is آمدن and its present stem is آی. When we attach the present tense prefix می, we keep the hat symbol over the آ to show it keeps the long a sound, making می‌آیند.

Is the word مراسم singular or plural?