Can I apply to positions with start dates that are earlier than my current contract end date?

Is it ok to apply for a position if you know you will not be available for the position's start date? I am currently in the middle of a teaching contract, so I wouldn't be able to start a position until Aug 2016. However, there are some jobs with start dates in Dec/Jan 2015 that I am interested in. Can I apply in case they do not find anyone or should I leave it alone? Please advise.