Questions & Answers about No vayamos a la marcha. Es peligrosa.
Why do we use vayamos here instead of vamos?
To say "let's not" do something, Spanish uses the negative present subjunctive. The verb ir (to go) is a special case: the affirmative "let's go" uses the indicative vamos, but the negative "let's not go" strictly follows the rule and uses the subjunctive form no vayamos.
Where does the word vayamos come from?
It is the nosotros (we) form of the verb ir (to go) in the present subjunctive. Because ir is highly irregular, its subjunctive forms use a completely different base, starting with vay- (such as vaya, vayas, and vayamos).
Why is it peligrosa and not peligroso?
Adjectives must agree in gender with the nouns they describe. Here, the adjective describes la marcha (the protest or march), which is a feminine noun. Therefore, the word for dangerous must take the feminine ending to become peligrosa.
Why isn't there a word for "It" before Es peligrosa?
Spanish almost always drops subject pronouns for inanimate objects like "it" because the verb and context do the heavy lifting. The verb Es (is) combined with the feminine adjective peligrosa makes it obvious that the sentence is referring back to la marcha.