When is it necessary or preferable to use 'in the' before a time period? Is one sentence more formal? Does the length of time matter?
Example 1: He was born last century. Example 1a: He was born in the last century.
Example 2: He was born last week. Example 2b: He was born in the last week.
Example 3: His birth was last century. Example 3a: His birth was in the last century.
Example 4: He was born middle of the night. Example 4a: He was born in the middle of the night.
To me, examples 1 and 3 sound better with 'in the', but I don't know why.