Learn Farsi: این کاغذها کثیف است.

In Farsi, when a pointing word like "this" (این) or "that" (آن) comes right before a noun to describe it, it always stays in the singular form, even if the noun itself is plural. So we say این کاغذها (literally "this papers") instead of using a plural form for "these".

How does the regular plural marker ها attach to the word کاغذ?

The suffix ها is the standard regular plural marker in Farsi. You simply add it to the end of a singular noun. Here, کاغذ (paper) becomes کاغذها (papers). In writing, it can be attached directly to the word or written with a tiny gap (a half-space) between them, but it is always pronounced as a single word.

Why does the sentence use the singular verb است (is) when we are talking about plural "papers"?

This is a very important rule in Farsi! When the subject of a sentence is a plural inanimate object (things that are not people or animals, like papers), the verb is almost always in the singular form. So, Farsi literally says "These papers is dirty."

Why isn't کثیف (dirty) attached to کاغذها with an ezafe (the short "e" sound)?

We only use the ezafe to link a noun directly to its adjective to make a single phrase (like "the dirty papers"). In this sentence, کثیف is stating a fact about the papers across a whole sentence. The sentence says "These papers dirty," with the subject () followed by the describing adjective () and ending with the verb ().