Learn Spanish (Latin America): No podemos ignorar el envejecimiento de la población. - We cannot ignore the aging of the population.

The current lesson is about el hecho de que. Why doesn't this sentence use it, and if we rewrote it to use that phrase, would it trigger the subjunctive?

This sentence avoids a complex clause by just using the noun el envejecimiento. If you rephrased it to No podemos ignorar el hecho de que la población..., you would actually use the indicative (envejece or está envejeciendo) because you are acknowledging an undeniable reality. You use el hecho de que + subjunctive for subjective value judgments, such as Es preocupante el hecho de que la población envejezca (It is worrying that the population is aging). Using a direct noun is a great native-sounding trick to avoid tricky clauses altogether!

Why is 'aging' translated as envejecimiento rather than a gerund like envejeciendo?

In English, '-ing' verbs often act as nouns (gerunds), as in 'the aging'. In Spanish, the present participle (-ndo form) can never act as a noun. You must use either an infinitive or the specific noun form. Here, el envejecimiento is the dedicated noun for the process of aging.

I learned previously that ignorar means 'to not know'. Can it also mean 'to ignore' (deliberately pay no attention to)?

Yes! Traditionally, ignorar means 'to be unaware of' or 'to not know' (for example: Ignoro por qué se fue - I don't know why he left). However, due to English influence, using ignorar to mean 'to deliberately ignore or disregard' is now universally understood and very common in everyday Spanish across Latin America.