1 not used in progressive tenses : to know and remember (someone or something) because of previous knowledge or experience
I didn't recognize you at first with your new haircut.
I can always recognize him from far away by/from the way he walks.
They recognized the odor at once.
2 : to accept or be aware that (something) is true or exists
It's important to recognize [=be aware of] your own faults.
They started talking and quickly recognized [=realized] how much they had in common.
3 : to accept and approve of (something) as having legal or official authority
The U.S. government has now recognized the newly formed country.
They refused to recognize the treaty.