すぎる

0. Meaning
The auxiliary suffix 〜すぎる means 'too much', 'excessively', or 'over-'. Note that when used as an auxiliary suffix attached to another word, it is generally preferred to write it in hiragana (すぎる) rather than kanji (過ぎる).

1. Conjugation Rules
〜すぎる conjugates like a standard Ichidan (ru-verb) (e.g., すぎない, すぎます, すぎた, すぎて). However, it attaches to other words using the following rules:

• Verbs: Use the ます-stem. (e.g., 食べます → 食べすぎる)
• い-Adjectives: Drop the final 〜い. (e.g., 高い → 高すぎる)
• な-Adjectives: Attach to the dictionary stem of the な-adjective. (e.g., 静か → 静かすぎる)
• Nouns: In colloquial speech, it can attach to nouns that describe a quality (e.g., 子供すぎる). It does not mean 'too much [noun]', but rather takes on a metaphorical or adjectival meaning (e.g., 子供すぎる means 'too childish'). This is not standard for all nouns.
• 〜たい (Want to): In highly colloquial speech or internet slang, it conjugates like an い-adjective, dropping the い before adding すぎる (e.g., 食べたい → 食べたすぎる / 'I want to eat it so badly'). This is not considered standard prescriptive grammar.

2. Special Cases for Negatives and 〜ない

• いい (Good): Always becomes よすぎる.
• ない (Non-existent/Negative): Becomes なさすぎる.
• Adjective Negatives: Standard adjective negatives use the standalone ない as an auxiliary, so they take the なさすぎる form (e.g., 高くない → 高くなさすぎる).
• Verb Negatives: When attaching to the ない form of verbs, dropping the い (e.g., 食べない → 食べなすぎる) is traditionally considered the standard form. However, inserting 'さ' (e.g., 食べない → 食べなさすぎる) is a highly common colloquialism (さ入れ言葉) that you will frequently hear in modern Japanese.
• 1-Mora Verb Stems: For verbs where the negative stem is only one mora (e.g., する, 来る, 見る, 居る, 出る), the standard rule requires inserting 'さ' (e.g., する → しなさすぎる, 見る → 見なさすぎる). Omitting the 'さ' is considered grammatically incorrect or highly unnatural.
• Adjectives ending in 〜ない: True adjectives like 少ない（すくない） and 汚い（きたない） drop the い (少なすぎる, 汚すぎる). For adjectives where 'ない' functions as a suffix indicating absence or a negative state, they take the なさすぎる form (e.g., 仕方ない → 仕方なさすぎる, 申し訳ない → 申し訳なさすぎる, 情けない → 情けなさすぎる). For adjectives derived from phrases, like もったいない, both もったいなすぎる and もったいなさすぎる are widely accepted and structurally correct.

3. The Noun Form: 〜すぎ
By using the stem form 〜すぎ, the compound becomes a noun. This is frequently used with the copula or as the subject of a sentence.
Example: 飲みすぎです (I drank too much / That's drinking too much).
Additionally, it is often used as a standalone casual exclamation (e.g., 「高すぎ！」 "Too expensive!").

4. Particles Remain Unchanged
When attaching 〜すぎる to a verb, the original particles of the sentence remain unchanged. For example, ケーキを食べる (eat cake) becomes ケーキを食べすぎる (eat too much cake).

5. Grammatical Function
When attached to an adjective or an intransitive verb, the entire compound functions as an intransitive verb. When attached to a transitive verb, it inherits that transitivity. In all cases, it conjugates like a verb, meaning you must use verb rules for past tense (〜すぎた), negative forms (〜すぎない), and the te-form (〜すぎて - did too much, and so...).

6. Nuance and Usage
Traditionally, this pattern implies a negative result or that something is 'beyond the proper limit.' However, in modern casual conversation, it is common to use it for positive traits, such as 可愛すぎる (too cute). Warning: Do not use 〜すぎる as a simple replacement for 'very' (とても) in standard or formal Japanese. Because of its inherent negative nuance of 'excess,' using it as a compliment can sound insulting or unnatural (e.g., telling a host their food is 美味しすぎる or a gift is 高すぎる might imply it is inappropriately so).

7. Disambiguation Warning
Do not confuse the negative form of this grammar point (e.g., 食べすぎない = 'don't eat too much') with the N2 grammar point 〜に過ぎない (merely / nothing more than), which is used differently (e.g., 学生に過ぎない = 'merely a student').