迷ったら a lot of。可算にも不可算にも使えて、肯定文で自然です。much(不可算)と many(可算)の主戦場は否定文・疑問文(not much / How many ...?)。肯定の平叙文で much を裸で使うと硬く響く——これがこの3つの実戦配置です。
When in doubt, a lot of: it works with countables and uncountables alike, and it's the natural choice in positive sentences. Much (uncountable) and many (countable) do their best work in negatives and questions — not much, How many …? A bare much in a positive statement sounds stiff. That's the whole deployment map.
実戦配置で覚える
Learn the Deployment, Not Just the Rule
教科書は「much =不可算、many =可算」で終わりがちですが、実戦で効くのはもう1軸。肯定文の「たくさん」は a lot of が標準で、much・many は否定・疑問で輝きます: I don't have much time.(あまり時間がない)/ How many people came?(何人来た?)。so much / too much のように強めの言葉が付けば、肯定文でも自然になります。
Textbooks stop at "much for uncountables, many for countables," but the axis that matters in practice is sentence type. Positive statements default to a lot of, while much and many shine in negatives and questions: I don't have much time. How many people came? Add an intensifier — so much, too much — and they turn natural in positive sentences too.
それぞれの持ち場Each word at its post
I have aなぜ a なのか【決まった数量表現】a few / a little / a lot of / a couple of / a bit のように、a ごとで「少し」「たくさん」を表す形。one の意味はまったく無い。 lot of homework tonight.
今夜は宿題がたくさんある。
肯定文の標準は a lot of。Positive statements run on a lot of.
We don't have much time.
あまり時間がない。
否定文の much =「あまり〜ない」。Negative much = "not a lot."
How many languages do you speak?
何か国語を話せるの?
疑問文の many。数を聞く定番。Question many — the counting question.
much + 不可算
time・money・water など、量ではかる名詞に。For measured stuff: time, money, water.
文法的に誤りではありませんが、肯定の平叙文で裸の much は硬く、書き言葉的に響きます。会話は a lot of(またはくだけて lots of)。so much homework(こんなに多い)のように強調が付けば自然です。
Not ungrammatical, just stiff. A bare much in a positive statement sounds bookish; conversation wants a lot of (or the even looser lots of). With an intensifier — so much homework — it turns natural again.
How much is it?いくらですか?値段は不可算の量。買い物の最重要フレーズ。Price is measured, not counted — shopping's key phrase.
so much / too muchこんなにたくさん/多すぎる強調が付いた much は肯定文でも自然。Thank you so much. もこの仲間。Intensified much lives happily in positives — Thank you so much included.
plenty ofたっぷりの(足りるほど)「十分ある」という安心感つきの「たくさん」。We have plenty of time.Abundance with reassurance built in: We have plenty of time.
lots ofどっさりのa lot of のさらにくだけた姉妹形。会話・メッセージ向け。A lot of's looser sibling — texts and chat.
まとめ / Summary
肯定文の「たくさん」= a lot of が標準。Positive "lots" = a lot of.
much(不可算)・many(可算)は否定・疑問が主戦場。Much and many work best in negatives and questions.
so much / too much なら肯定文でも自然。So much and too much are fine anywhere.
How much =量・値段、How many =数。How much asks amount and price; How many asks number.