Here's why:
* It names a state of being: Ignorance refers to a lack of knowledge or information.
* It can be the subject of a sentence: "Ignorance is bliss" (Ignorance is the subject of this sentence).
* It can be the object of a verb or preposition: "He was filled with ignorance" (ignorance is the object of the preposition "with").
Let me know if you'd like to explore more parts of speech!