shin

ش

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

finalmedialinitialisolated
ـشـشـشـش

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

ش

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

شـ

For example these words:

drinking
shurb
شُرب
bay
sharm
شَرم
longing
shawq
شَوق

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.

ـشـ

For example these words:

wood
khashab
خَشَب
passion
3ishq
عِشق
comb
mishT
مِشط

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

ـش

For example these words:

nest
3ushsh
عُشّ
straw
qashsh
قَشّ
monster
waHash
وَحَش

Now you know that:

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

The letter shin 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.

شـ

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

ش

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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