Questions & Answers about ما باید بررسی کنیم که این خاک تا چه اندازه حاصلخیز است.
Could we use تا چه حد (tâ che hadd) instead of تا چه اندازه (tâ che andâze) in this sentence?
Yes, absolutely. تا چه حد and تا چه اندازه are virtually interchangeable in this context. Both translate to "to what extent." اندازه literally means "size" or "measure," while حد means "limit" or "boundary," but functionally they do the exact same job when asking about the degree of something.
Why do we need the word که (that) right before the question word? English just says "examine to what extent."
In Persian, که is widely used as a conjunction to introduce subordinate clauses, including indirect questions. While English drops "that" before a question word (we wouldn't say "examine that to what extent"), Persian naturally includes که to smoothly link the main verb (بررسی کنیم) to the dependent clause explaining what is being examined.
Why is the verb بررسی کنیم (we examine) in the subjunctive mood here?
It is in the subjunctive because it is triggered by باید (must). Whenever you use a modal verb of necessity or obligation like باید or شاید (might), the following verb must take the subjunctive mood. Because بررسی کردن (to examine) is a compound verb, the subjunctive mood is applied to the verbal part (کردن), resulting in بررسی کنیم.
How is the word حاصلخیز (fertile) built?