kono kikai ha hurui desu ga, mada tukaemasu.

は marks 機械 as the topic of the sentence.

So この機械は means:

• as for this machine
• this machine, ...

The sentence is not just identifying the machine; it is making a comment about it:

• この機械は = as for this machine
• 古いですが、まだ使えます = it is old, but it can still be used

A very literal breakdown is:

• この機械は = as for this machine
• 古いです = is old
• が = but
• まだ = still
• 使えます = can be used / can use

No. This が is not the subject marker.

Here, が works like:

• but
• although
• though

So:

• 古いですが、まだ使えます = It is old, but it can still be used.

Japanese has more than one が:

1. Subject-marker が

   • example: 猫がいます = There is a cat.

2. Conjunction が

   • example: 古いですが、まだ使えます = It is old, but it still works/can still be used.

You can tell which one it is from the structure of the sentence.

They can.

• 古い。 = It is old.
• 古いです。 = It is old. / It’s old.
  (more polite)

So in this sentence, です is adding politeness.

This is very common:

• 高いです = It is expensive.
• 新しいです = It is new.
• 古いです = It is old.

In other words:

• 古い = plain style
• 古いです = polite style

Yes, 古いです is normal and grammatical in modern Japanese.

The point that sometimes confuses learners is this:

• with a noun or な-adjective, です acts like the polite copula
• with an い-adjective, the adjective itself already carries the meaning of is

So:

• 静かです = is quiet
• 学生です = is a student
• 古いです = old + politeness

You do not need to think too hard about that for everyday use. For learners, the practical rule is:

• い-adjective + です = polite sentence

That is exactly what is happening here.

まだ means still in this sentence.

So:

• まだ使えます = can still be used

It suggests that even though the machine is old, its usefulness has not ended.

A common contrast is:

• まだ = still
• もう = already / anymore, depending on the sentence

For example:

• まだ使えます = It can still be used.
• もう使えません = It can no longer be used.

So まだ gives the sentence the nuance of surprisingly, it still works / is still usable.

Yes.

The dictionary form is:

• 使う = to use

The potential form is:

• 使える = can use / be able to use

The polite form is:

• 使えます

So:

• 使う → 使える → 使えます

In this sentence, 使えます means that the machine is still usable.

Because the sentence is not saying someone uses the machine. It is saying that the machine can still be used.

The topic is already この機械は, so Japanese does not need to add an object here.

A literal English-style version might look like:

• As for this machine, it can still be used.

Japanese often leaves out things that are understood from context.

If you wanted to explicitly say someone can use this machine, you might say something like:

• この機械をまだ使えます
  • this is possible in some contexts, but it focuses more on being able to use the machine
• この機械はまだ使えます
  • this sounds more like the machine is still usable

So the original sentence is natural for talking about the machine’s condition.

Yes, depending on context.

By itself, 使えます can mean:

• can use
• is usable
• can be used

In this sentence, because the topic is this machine, the natural interpretation is:

• This machine can still be used
• This machine is still usable

It does not usually mean I can still use this machine unless the context strongly points to I as the understood subject.

So context decides the most natural English translation.

Because この must directly modify a noun.

• この + noun
• この機械 = this machine

By contrast:

• これ = this one / this

So:

• この機械 = this machine
• これは機械です = this is a machine

A useful pattern:

• この = this + noun
• その = that + noun
• あの = that over there + noun

and

• これ = this one
• それ = that one
• あれ = that one over there

Yes — and that is how Japanese is normally written.

Natural Japanese writing would be:

この機械は古いですが、まだ使えます。

The spaces in your version are only there to help learners see the parts more easily. In real Japanese text, words are usually not separated by spaces.

So:

• learner-friendly: この　機械　は　古い　です　が、　まだ　使えます。
• normal writing: この機械は古いですが、まだ使えます。

Also, です and が would normally appear together as ですが with no space.

が and でも can both express contrast, but they are used differently.

In this sentence:

• 古いですが、まだ使えます = It is old, but it can still be used.

Here が connects two parts of one sentence in a smooth, slightly formal or neutral way.

でも is also possible, but it usually starts a new sentence or creates a stronger break:

• この機械は古いです。でも、まだ使えます。 = This machine is old. But it can still be used.

So the difference is roughly:

• ですが = smoother connection inside one sentence
• でも = more separate, like starting a new sentence with but

Both are understandable, but ですが fits the original sentence structure better.

A natural casual version would be:

この機械は古いけど、まだ使える。

Changes:

• 古いです → 古い
• が → けど
• 使えます → 使える

So:

• polite: この機械は古いですが、まだ使えます。
• casual: この機械は古いけど、まだ使える。

You might also hear:

• この機械、古いけどまだ使える。

In casual speech, は is sometimes omitted when the topic is obvious.

Yes. The sentence has a mild contrast:

• 古い = old
• まだ使えます = still usable

So the feeling is:

• Even though it’s old, it’s still usable
• It may be old, but it still works

The speaker is not just listing two facts. They are pointing out that the second part is a little unexpected or noteworthy.

That contrast is exactly why が and まだ work so well together here.