سلسلة الدراجة قديمة، إذن يساوم المشتري البائع.

Because this is an iḍāfa construction, often called a construct phrase.

• سلسلة = chain
• الدراجة = the bicycle

In an iḍāfa:

• the first noun usually does not take ال
• the second noun tells you whose/what kind
• the whole phrase can still be definite

So سلسلة الدراجة literally means chain of the bicycle, which in natural English is the bicycle chain.

Also, the second noun in an iḍāfa is grammatically genitive. So if full case endings were written, it would be الدراجةِ.

Because سلسلة ends in ة (tāʾ marbūṭa).

When a word with ة is said by itself at a pause, it usually sounds like -a or -ah. But when it is connected to another word in an iḍāfa, the ة is pronounced as -t.

So:

• by itself: سلسلة ≈ silsila
• in سلسلة الدراجة: silsilat ...

You may also hear الدراجة pronounced with an assimilated ال because د is a sun letter, so الدراجة sounds like ad-darrāja, not a clear al-darrāja.

Because سلسلة is a feminine noun, and the adjective must agree with it in gender.

• سلسلة = feminine
• so the adjective must also be feminine: قديمة

If the noun were masculine, you would use قديم.

This is normal adjective agreement in Arabic.

Because here قديمة is not an attributive adjective inside the noun phrase. It is the predicate of the sentence.

The sentence structure is:

• سلسلة الدراجة = the bicycle chain
• قديمة = old

So the whole sentence means The bicycle chain is old.

In Arabic, the predicate in this kind of present-tense nominal sentence is usually indefinite, so قديمة does not take ال.

Compare:

• السلسلة القديمة = the old chain
  
  • just a noun phrase
• السلسلة قديمة = the chain is old
  
  • a complete sentence

Because Arabic usually does not use a present-tense verb meaning is/are in sentences like this.

So:

• سلسلة الدراجة قديمة literally looks like the bicycle chain old
• but it means The bicycle chain is old

This is called a nominal sentence in Arabic.

If you wanted the past tense, then Arabic would use a verb such as كان:

• كانت سلسلة الدراجة قديمة = The bicycle chain was old

Here إذن means so, then, or therefore.

It connects the first idea to the result:

• The bicycle chain is old
• therefore / so
• the buyer bargains with the seller

So it signals a conclusion or consequence.

Also, do not confuse إذن with إذا:

• إذن = so / therefore
• إذا = if / when

يساوم means he bargains, he negotiates, or he haggles.

It comes from a verb that often has the sense of negotiating over a price. In this sentence, the idea is that the buyer tries to get a better deal because the chain is old.

As for tense, Arabic non-past forms like يساوم can mean:

• is bargaining
• bargains
• sometimes even will bargain, depending on context

Here the most natural meaning is present: the buyer bargains / is bargaining.

Because verb–subject–object order is very common in Modern Standard Arabic.

So:

• يساوم = bargains
• المشتري = the buyer
• البائع = the seller

This order is completely normal in MSA.

Arabic can also use subject–verb–object:

• المشتري يساوم البائع

That is also grammatical. The version with the verb first is just a very standard MSA pattern.

There are two main clues:

1. Word order
   In a normal verb–subject–object sentence, the noun right after the verb is usually the subject, and the next noun is the object.

2. Case endings
   In fully vocalized Arabic, the subject would be nominative and the object accusative. In everyday printed Arabic, these endings are usually not written, so learners often rely on word order and context.

So here:

• المشتري = the one doing the bargaining
• البائع = the person being bargained with

Because the sentence is talking about specific roles in a known situation: the buyer and the seller involved in this sale.

Arabic often uses ال in places where English might or might not use the, especially when the people or things are understood from context.

So this sounds natural in Arabic:

• المشتري = the buyer
• البائع = the seller

It does not necessarily mean they were previously mentioned by name; it can simply mean that the situation already makes them identifiable.