Breakdown of Нам не пройти этим непроходимым болотом!
не
not
мы
we
этот
this [f: эта, n: это]
пройти
to pass (perfective)
Questions & Answers about Нам не пройти этим непроходимым болотом!
Why is этим непроходимым болотом in the instrumental case without a preposition like через?
This is the bare Instrumental of Route. You can often describe movement through or across a space by putting the noun describing that space directly into the instrumental case, with no preposition. It is especially common with natural terrain like a field (полем), a forest (лесом), or a swamp (болотом).
Why does the sentence use the dative Нам and the infinitive не пройти instead of just saying Мы не можем пройти?
Using a dative subject plus a perfective infinitive with не is an idiomatic way to express absolute impossibility due to external circumstances. While Мы не можем пройти means simply "We cannot pass," Нам не пройти feels much stronger: "There is absolutely no way for us to get through."
Could I use по + dative here, like по этому непроходимому болоту?
Yes, you could. Using по + dative is very common for movement along a surface. However, the bare instrumental (этим болотом) emphasizes the terrain itself as the route you are attempting to take, which pairs perfectly with the adjective непроходимым (impassable).
Are the words пройти and непроходимым related?