From BOL:

bit
Integer data type 1, 0, or NULL.


>I would say the bit type is a logical data type in SQL Server. Only possible values of 0 or 1.
>
>>The datetime fields cannot be empty in SQL Server. Usually NULLs are used instead in which case IS NULL operator cabn be used.
>>There're no logical data type in SQL Server. You can use any integer field instead.
>>

IF someDateField IS NULL
>>...
>>IF someLogicalField = 0
>>

>>