Aregulatory practice in which the benefits are weighted against the costs of certain actions, which in turn can be compared to other possible solutions is called

The difference is how the time can affect the concept of both.

In History a theme is a repeating moment, a common idea that keep repeating itself in the past. This is called theme.

A period is a time when the themes were set in. The period represents a specific time were something occurred, with a specific beginning and ending.

The theme can be found in different times.