Can We Switch from Married Filing Joint one year to Married Filing Separate the Next?

The short answer: Yes.  But you cannot switch your filing status from MFJ to MFS (separate) in the same year beyond the return due date (April 15th).  You also may not amenda previous years from MFJ to MFS.  You may however always change your filing status of the current year and past 3 years from MFS to MFJ.

I tried to out this as simply as can be but honestly this is exactly how it reads below:

Joint Return After Separate Returns

You can change your filing status from a separate return to a joint return by filing an amended return using Form 1040X.

You generally can change to a joint return any time within 3 years from the due date of the separate return or returns. This does not include any extensions. A separate return includes a return filed by you or your spouse claiming married filing separately, single, or head of household filing status.

Separate Returns After Joint Return

Once you file a joint return, you cannot choose to file separate returns for that year after the due date of the return.

REFERENCE: Pub 17 (2014)

http://www.irs.gov/publications/p17/ch02.html#en_US_2014_publink1000170792