kono houtyou ha hurui desu ga, mada yoku kiremasu.

この is a determiner, so it directly modifies a noun:

• この 包丁 = this knife

By contrast:

• これ = this one / this thing

So これの 包丁 is not the normal way to say this knife. If you want to put a word directly before a noun, use この / その / あの.

は marks the topic of the sentence:

• この包丁は = As for this knife, ...

The sentence is making a comment about the knife:

• it is old
• but it still cuts well

Using は is very natural here because the knife is the thing being talked about.

If you used が, it would sound more like you are specifically identifying this knife as the one with that property, rather than simply talking about it as the topic.

古い is an i-adjective. With i-adjectives, the い stays:

• 古い = old
• 古いです = is old / old (polite)

So you do not say:

• 古です ✘

That would be incorrect.

A useful comparison:

• 高いです = expensive / high
• 新しいです = new
• 古いです = old

The です adds politeness; it does not replace the い.

Here, が means but:

• 古いですが、まだよく切れます。
• It’s old, but it still cuts well.

This が connects two clauses and shows contrast:

1. 古いです = it is old
2. まだよく切れます = it still cuts well

So the idea is: even though it is old, it remains effective.

In everyday speech, learners will also hear けど or けれども used in similar ways.

Here, まだ means still.

• まだ よく 切れます = still cuts well

This is an important word because まだ can mean different things depending on whether the sentence is positive or negative:

• まだ切れます = it still cuts
• まだ切れません = it doesn’t cut yet / it still can’t cut

So in this sentence, because the verb is affirmative, まだ means still.

よく is the adverb form of いい in this usage, and here it means well:

• よく切れます = cuts well

It describes how the knife cuts.

Compare:

• 日本語をよく話します = speaks Japanese well
• このはさみはよく切れます = these scissors cut well

So よく modifies the verb 切れます.

This is a very common learner question.

• 切ります usually means to cut something
• 切れます can mean can cut or, with things like knives/scissors, cuts well / is sharp enough to cut

In this sentence, the knife itself is the topic:

• この包丁はまだよく切れます
• literally something like This knife still cuts well

Japanese often uses 切れる for the performance or sharpness of a blade. So this sentence is not really focusing on a person cutting something; it is describing the knife’s condition and usefulness.

That is why 切れます sounds natural here.

Historically and grammatically, 切れる can be understood as related to the potential idea of being able to cut, but in sentences about knives, scissors, and blades, it often functions almost like to cut well / to be sharp.

So in this sentence:

• まだよく切れます

the most natural interpretation is:

• it still cuts well
• it’s still sharp enough to cut well

You do not need to think of it as a literal English-style can every time. It is often just the normal Japanese way to describe whether a blade works effectively.

Japanese often leaves out information that is obvious or not important.

Here, the point is not what the knife cuts. The point is the knife’s general condition:

• it is old
• but it still works well

So よく切れます means something like:

• it cuts well
• it’s still sharp
• it still works well as a knife

An object is unnecessary because the sentence is making a general statement.

Because the two parts use different kinds of predicates:

• 古いです → adjective + polite です
• 切れます → verb in polite ます form

So the sentence combines:

1. an adjective statement
2. a verb statement

Both are polite, but they use different endings because one is an adjective and the other is a verb.

Yes. A casual version would be:

• この包丁は古いけど、まだよく切れる。

Changes:

• です → dropped in casual speech
• が → often replaced by けど
• 切れます → 切れる

So:

• polite: この包丁は古いですが、まだよく切れます。
• casual: この包丁は古いけど、まだよく切れる。

Both mean basically the same thing.

Yes, that nuance is very likely.

Because of が (but) and まだ (still), the sentence suggests a contrast:

• you might expect an old knife not to work well
• however, this one still does

So the speaker is not just describing the knife mechanically; they are also expressing a mild sense of unexpected usefulness.

In this sentence, 古い most naturally means old in age or long-used condition.

For objects, 古い can mean:

• old in age
• not new
• worn from long use

So for a knife, it suggests the knife has been around for a long time, not that it is necessarily bad. The second clause shows that clearly:

• it’s old, but it still cuts well

So old here does not mean useless.