know which is which

and tell which is which

to be able to distinguish one person or thing from another person or thing. I have an old one and a new one, but I don't know which is which. I know that Bill and Bob are twins, but I can't tell which is which.

Common Names:

Name	Pronounced	Usage
Wynn	[win]
Ebbe	EB-be (Swedish), E-bə (German)	Danish, Swedish, Norwegian, German (Rare)
Ceara	-	English (Rare)
Bharath	-	Tamil, Indian, Malayalam, Telugu
CustÓDia	-	Portuguese
Merrill	MER-əl	English