Amazing Chinese Characters (526) Sentence - 句 and Hook - 勾

 The shell bone script of the character Hook or Sentence is

The middle is character Mouth - 口 (Post 16), the two L alike are hooks. It means that the hooks hook mouth, e.g. fish mouth). 汉典（ Chinese Dictionary) says that the character Hook was same as character Sentence, which I guess that the sentence is hooked by words logically, the hook is hooked physically.

Other dictionaries don't have shell bone, bronze scripts of character Hook, they count the older scripts are just for character Sentence, not for Hook. 

I agree with 汉典 (Chinese Dictionary). I think that the meaning of Hook may be a little bit earlier than that of sentence, because hook is physical characteristics, visible. Sentence is flow of thinking, logical, not directly visible. I think that shell bone script is more to be Hook meaning.

The bronze script of the character is 

Hooks are on the top, and mouth is on the bottom. 

The big seal script of the character is

Similar to bronze script. 

The small seal script of the character is

The top hook is distorted, the lower hook changes a little.

The clerical script of character Hook is

The outside are two hooks, but the top hook is not like a hook anymore. The inside 厶 means "small", implying that the hooks are small.

The clerical scrkpt of character Sentence is

Inside is 口, not 厶 . Sentence is related to people speech (Mouth, 口). The two characters finally are completely distinguished each other at the Han Dynasty (About 202 B.C.  - 220 A.D.) when the communication became very important, one character has two different related meanings, which caused too much confusion. They must be distinguished without any delay.

The Pinyin for character Hook - 勾 is Gou1. The Pinyin for character Sentence - 句 is Ju4.