jim

ج

The Arabic letter jim can appear in four different forms: isolated, initial, medial and final.

finalmedialinitialisolated
ـجـجـجـج

When you show the letter on its own, you use the isolated form.

ج

When the letter is the first letter of a word, you use the initial form.

جـ

For example these words:

body
jasad
جَسَد
wound
jurH
جُرح
root
jidhr
جِذر

When the letter is not the first and not the last but somewhere in the middle of a word, you use the medial form in most cases.

ـجـ

For example these words:

dimension
Hajm
حَجم
prison
sijn
سِجن
stone
Hajar
حَجَر

When the letter is the last letter of a word, you use the final form in most cases.

ـج

For example this word:

snow
thalj
ثَلج

Now you know that:

In most cases...
Let us look at the other cases!

The letter jim has dual joining, like most Arabic letters. It wants to join with both the letter before it and the letter after it.
But some letters has right joining. They only want to join with the letter before it (which is the letter to the right since Arabic is written from right to left).

When the letter is in the middle of a word, and follows a right joining letter, you use the initial form.

جـ
face
wajh
وَجه
pain
waja3
وَجَع
because of
'ajl
أَجل

When the letter is the last letter of a word, and follows a right joining letter, you use the isolated form.

ج
tower
burj
بُرج
ivory
3aaj
عَاج
stair
daraj
دَرَج

Now you know that:

That's it!
The rules you just learned can be applied to all Arabic letters with dual joining, which is most of them.

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