だけ

だけ is a versatile particle used to express a limit. Its primary function is to define a scope: 'only this' or 'just that.'

1. How to attach it:

• Nouns: Directly attached for present states. For past states, the past-tense copula can come before or after だけ, which changes the meaning. (e.g., 水（みず）だけ - Only water; 学生（がくせい）だけだった - It was only students; 学生（がくせい）だっただけ - Was just a student)
• Verbs: Attached to the plain form (dictionary, past, potential, continuous 〜ている, or negative 〜ない). (e.g., 見（み）ているだけ - Just looking)
• い-Adjectives: Attached to the plain form. (e.g., 広（ひろ）いだけ - Just spacious)
• な-Adjectives: Use な for the present affirmative, but past tense (だった) or formal copulas can also precede it. (e.g., 静（しず）かなだけ - Just quiet; 静（しず）かだっただけ - Was just quiet)

2. Particle Interaction:
だけ can either replace or be used alongside other particles. It often replaces the topic marker は, subject marker が, and object marker を, but it can also be followed by them (だけが or だけを) for extra emphasis. For case particles like に, で, and と, だけ can either precede or follow them depending on the context (e.g., あなたにだけ or あなただけに - only to you). Note that with the means/method particle で, the order changes the core meaning: だけで means 'just by / using just' (e.g., バスだけで行（い）ける - You can get there using just a bus), while でだけ means 'only by' (e.g., バスでだけ行（い）ける - You can get there only by bus). Furthermore, while both can mean 'only to [target]', だけに also has a distinct advanced usage meaning 'precisely because' (〜だけに). Additionally, combining だけ with は creates the common pattern だけは, meaning 'at least' (e.g., これだけは覚（おぼ）えてください - Please remember at least this).

3. Expressing Maximum Limit ('As much as'):
When paired with verbs expressing desire or potential, だけ indicates the maximum limit of an action. In this context, it translates to 'as much as' or 'to the extent of.'

• 食（た）べたいだけ食（た）べてください。(Please eat as much as you want to eat.)
• できるだけ早（はや）く来（き）てください。(Please come as fast as you can.)

4. だけで (Just by doing...):
When combined with で, it can mean 'just by' doing something or 'just with' something.

• 見（み）るだけでいいです。(Just by looking is fine.)

5. 〜ば〜だけ (The more... the more):
Similar to 〜ば〜ほど, using a conditional form followed by the same verb with だけ expresses 'the more you do X, the more Y.'

• 読（よ）めば読（よ）むだけわかります。(The more you read, the more you understand.)

6. Not only... but also:
When combined with the negative form, it creates the pattern だけでなく (or だけでなく〜も), meaning 'not only... but also.'

• 彼（かれ）は英語（えいご）だけでなく、日本語（にほんご）も話（はな）せます。(He can speak not only English but also Japanese.)

7. Nuance and Advanced Usages:
だけ is neutral and can be used with affirmative or negative verbs. If you want to express a negative feeling about a limitation (that something is 'not enough'), use しか〜ない instead. Crucially, しか MUST be paired with a negative verb, whereas だけ does not have this restriction (e.g., 水（みず）だけ飲（の）む - I drink only water vs. 水（みず）しか飲（の）まない - I drink nothing but water). In formal or written Japanese, the particle のみ is often used as a more stiff equivalent to だけ. Additionally, だけ appears in advanced expressions like 〜だけあって (as expected of) and 〜だけに (precisely because).

8. Comparison with similar particles:
While だけ sets a strict boundary, ばかり suggests that something is the only thing happening or present in a more subjective, often repetitive way.