Learn Farsi: این نظریه بین مردم مقبول است. - This theory is accepted among the people.

مقبول (maqbul) uses the Arabic maf'ul (ma-C1-C2-u-C3) pattern, which creates a passive adjective or noun referring to the thing receiving the action. The root consonants are ق-ب-ل (q-b-l). Because the root relates to accepting, مقبول literally translates to accepted.

What is the three-letter root for مقبول, and what other common Farsi words share it?

The root is ق-ب-ل (q-b-l), which carries the core meaning of acceptance or facing. You already know this root from everyday words like قبول (qabul - acceptance), استقبال (esteqbal - welcoming), and مقابل (moqabel - opposite). Spotting these three letters helps you instantly connect the vocabulary.

Since مقبول means accepted, could I use it to say my credit card was accepted?

Not usually. مقبول is a slightly formal or literary word, making it perfect for an abstract concept like a نظریه (theory). For an everyday transaction like a credit card being accepted, you would typically use a compound verb like قبول کردن (qabul kardan) or پذیرفتن (paziroftan).

How is the word نظریه (theory) formed from نظر (opinion)?

It uses the Arabic suffix ـیّه (-iyye, usually pronounced -iye in modern Persian). This suffix is frequently added to Arabic roots to create abstract nouns or systems of thought. By adding it, نظر (view) becomes (theory).