The modal particle 矣
A modal particle (语气词) is a function word that adds additional semantic meanings to the sentence or emotionally colors it. It is usually placed at the end of a sentence.
We use the modal particle 矣 
to emphasize a categorical judgment. It is used in written speech.
to emphasize a categorical judgment. It is used in written speech.Examples
人生得一知己足矣
It is enough to have one soulmate in life
rénshēng de yì zhījǐ zú yǐ
他的想法可谓多矣
He has a lot of ideas
tā de xiǎngfǎ kěwèi duō yǐ
We also can use 矣 instead of 了 . It indicates the completion of an action or shows that the situation has changed and new circumstances have arisen.
. It indicates the completion of an action or shows that the situation has changed and new circumstances have arisen. Examples
此事准备久矣
It took a long time to prepare this case
cĭ shì zhŭnbèi jiŭ yĭ
王老矣
Wang has gotten old
wáng lǎo yǐ