What is the purpose of the suffix "さ" on adjectives?

Question

What is the purpose of the suffix "さ" on adjectives like 美しさ and 多さ? The former is the title of an essay by Banana Yoshimoto, so I don't have much context for it. The book editors translated it as "On beauty" which didn't help me understand what this さ business was all about. In the case of the latter, she writes: >"品揃えの多さについつい買い込んでしまい、大荷物を抱えて併設の花屋に行った。" Which I understand as: >"There were many goods there that, against my better judgement, I had purchased. Carrying the bags I went to the attached flower shop."

Answer 1

With i-adjectives, removing the final い and replacing it with さ turns the word into a noun. 美しい 、beautiful, becomes 美しさ、beauty, or 多い、plentiful, becomes 多さ、plenty. In the case of 美しさ、since it is the title of an essay apparently, it was just translated into English as "On Beauty," to make it more apparent in English what the subject of the essay will be. Personally, I think in English having the "On" in the title makes it sound like it will be a more philosophical text, but I don't see why a literal translation, simply "Beauty," wouldn't have been an acceptable title as well.

In your example sentence, 品揃えの多さについつい買い込んでしまった would mean that "due to their extensive selection, (he or she) ended up buying a lot"

Answer 2

If you put SA, then, adjectives become nouns.