Learn Hardcore Japanese: watasi ha atarasii megane wo kaitai.

は marks the topic of the sentence: what you’re talking about.
が normally marks the grammatical subject and often introduces new or contrasted information.

私は新しい眼鏡を買いたい。
→ As for me, (I) want to buy new glasses.

The speaker is presenting “me” as the topic of conversation. If you said:

私が新しい眼鏡を買いたい。

this would sound like you’re contrasting yourself with someone else, e.g. “I’m the one who wants to buy new glasses (not someone else).” It’s possible, but it has that added nuance and is less neutral than は here.

Can I drop 私 and just say 新しい眼鏡を買いたい。?

Yes, and that’s actually more natural in many real conversations.

Japanese often omits anything that’s clear from context: subjects, objects, even the topic. If it’s obvious that you’re talking about yourself, 新しい眼鏡を買いたい。 on its own usually means “I want to buy new glasses.”

So:

私 is kept when you:
- want to make the subject explicit (e.g. in writing, or to avoid confusion), or
- contrast yourself with others: 私は買いたいけど、彼は買いたくない。
  “I want to buy them, but he doesn’t.”

Why is を used after 新しい眼鏡?

を marks the direct object of a verb — the thing the action is done to.

Verb: 買う (to buy)
Object: 新しい眼鏡 (new glasses)

So 新しい眼鏡を買いたい literally structures as:

[new glasses] を [want to buy]

In English, word order shows that “glasses” is the object (“buy glasses”).
In Japanese, を does that job, so the position is more flexible as long as the particles are correct.

Does 眼鏡 (めがね) mean “glass” or “glasses”? Why no plural?

眼鏡 basically means “a pair of glasses” or “eyeglasses.” Japanese usually doesn’t mark singular/plural the way English does.

So:

眼鏡 could be translated as “a pair of glasses” or just “glasses.”
Context decides whether the English should be singular or plural.

If you need to be very explicit, you can say:

新しい眼鏡を一つ買いたい。 – I want to buy one pair of new glasses.
新しい眼鏡を二つ買いたい。 – I want to buy two pairs of new glasses.

But in everyday speech, just 眼鏡 is fine, and English will naturally translate it as “glasses.”

Why is 新しい placed before 眼鏡? Can I put it after, like in English?

In Japanese, adjectives that directly modify nouns come before the noun.

新しい眼鏡 – “new glasses” (literally “new glasses”)
There is no pattern like “glasses new” in standard Japanese.

So the general rule is:

adjective + noun
- 高い本 – an expensive book
- きれいな部屋 – a clean room
- おいしいケーキ – a delicious cake

You can describe something after the noun with a phrase or clause:

眼鏡が新しい。 – The glasses are new.
新しくなった眼鏡 – glasses that became new

But if it’s just “new X,” put the adjective directly in front: 新しい眼鏡.

What exactly does the ～たい in 買いたい mean, grammatically?

～たい is attached to the stem of a verb to express “want to do (that verb)” from the speaker’s perspective.

Dictionary form: 買う (to buy)
Stem: 買い
買い + たい → 買いたい – “want to buy”

Key points:

It expresses the speaker’s own desire (or that of someone in the same “inner circle” in casual speech).
With other people’s desires, ～たい can sound like you’re assuming their feelings. Often you’ll use other forms (e.g. ～たがっている) for that.

Basic patterns:

買いたい – want to buy
買いたくない – don’t want to buy
買いたかった – wanted to buy
買いたくなかった – didn’t want to buy

Is 買いたい present or future? How do you know the tense?

Japanese doesn’t distinguish present vs future the same way English does. 買いたい is non-past:

It can mean:
- “I want to buy (now / generally).”
- “I want to buy (in the future / sometime soon).”

Context usually tells you whether it’s about a current feeling, a future plan, or both.
To talk about a past desire, you’d use:

買いたかった – “I wanted to buy (but maybe I didn’t)”

How do I make this sentence more polite?

The given sentence is in plain style. To make it polite, you normally add です:

私は新しい眼鏡を買いたいです。

That’s standard polite speech. Some speakers avoid ～たいです and use an extra phrase:

私は新しい眼鏡を買いたいと思います。
– Lit. “I think I want to buy new glasses.” (sounds a bit softer, more formal)

In casual conversation with friends, you’d normally just say:

新しい眼鏡を買いたい。

What’s the difference between 新しい眼鏡を買いたい and 新しい眼鏡が欲しい?

Both can be translated as “I want new glasses,” but they focus on slightly different things.

新しい眼鏡を買いたい。
- Literally: “I want to buy new glasses.”
- Focus: the action of buying.
- Implies: you want to go and buy them (the process/action).
新しい眼鏡が欲しい。
- Literally: “New glasses are wanted (by me).”
- Focus: the thing you want (possession).
- Implies: you want to have new glasses; how you get them is not specified.

In many everyday situations, they overlap and either is fine, but:

Planning to go shopping → 買いたい feels more natural.
Talking about just wanting to have them, maybe as a wish → 欲しい can sound more natural.

Could I say メガネ instead of 眼鏡? Is there any difference?

Yes. メガネ (katakana) and 眼鏡 (kanji) both mean “glasses.”

In everyday writing (messages, casual notes), メガネ is very common.
眼鏡 is the standard kanji form and is common in more formal writing, books, or where kanji are preferred.

Spoken Japanese doesn’t distinguish them; they’re both pronounced めがね.
So:

私は新しいメガネを買いたい。 – This is completely natural in casual contexts.

Can I change the word order, like 私は買いたい新しい眼鏡を?

Not in that way. Japanese word order is much more flexible than English, but adjectives must stay right before the noun they modify, and verb phrases typically come at the end.

Some orders you might see:

私は新しい眼鏡を買いたい。 (default)
新しい眼鏡を私は買いたい。 (topicalizing “me,” adding a bit of emphasis)

But:

私は買いたい新しい眼鏡を。 – incorrect / very unnatural
私は新しいを眼鏡買いたい。 – incorrect

General rule to keep in mind:

Modifiers (like adjectives) go immediately before what they modify.
The main verb or verb phrase comes at the end of the sentence.