First, some recommendations:
There are two paths to having a double major. Which path will depend on whether each major grants a BA degree or BS degree or whether one grants a BA and the other a BS. So, for example, if your major is English and you want to add Philosophy as a major, then the only additional requirement over the English degree would be to take the required courses for the Philosophy degree, since all the other requirements will be the same (though some majors may recommend a specific minor). If, for an alternate example, you have a major in Physics and want to add a major in Philosophy, you will end up with two degrees, one in Physics and one in Philosophy. Don't panic on this latter case. It's not much different.
Two Degrees, you say? Both BA and BS degrees require minors and a certain number of courses to satisfy the major. The most notable difference between the two is that with the BA, each student is required to demonstrate proficiency in a foreign language, in addition to having a minor. Using the example above for a Physics major adding a Philosophy major, the Philosophy major, since it's a BA, would require you to demonstrate proficiency in a foreign language. You would be able to use either the Physics major or one of the other minors as a minor for the Philosophy major. So, staying with our example, the Physics major who wants to add a Philosophy major, in addition to taking all the classes required by the Philosophy degree, would also have to demonstrate proficiency in a foreign language. The bonus for this scenario is that you will come out of it with two degrees, rather than one.
Proficiency in a foreign language can be demonstrated in several ways. One means is to take four semesters of a language. For other options, see Procedures For Foreign Language Credit.
Where to start
This form is now online. However, when the form is submitted, your change of major is not immediately thereby complete. The form goes to an office and that office will enter the change in the computer system. They will then send you a notification that your major has been changed, generally in the form of an email to your MTSU email account. Depending on how busy the office is, the process could take several days. Be patient.
Upper Division Form (this form is specific to the Philosophy major)
The Upper Division Form is your intended plan of study and does not need to be filled out immediately upon changing majors, but should be filled out as early as you can (as a guideline: within the next three semesters). You should consult with your advisor in constructing this form. Once turned in, this form will act as a sort of contract between you and the University concerning your plan of study. The Upper Division Form will also help guide you in knowing how to fulfill the General Education classes needed.
If you rely on Pipeline/Raidernet to indicate who your advisor is, it will likely not assign you an advisor for your second major. That may be for the best, since you can then go to the department and ask what the policy is for choosing advisors. In the philosophy department you are free to pick your advisor.
How many classes/hours are required for the Major?
The number of classes and which specific classes must be taken may vary between departments. For the Philosophy major, 30 hours or ten classes in philosophy are required (in addition to a minor and foreign language proficiency). There are three classes within that ten, or 9 hours, that each major must successfully complete: 2110, 4010, and 4020. The remaining classes/hours are up to each student and the department offerings. It is worth noting that adding a second major will not typically exceed the 120 hour requirement for the degree. The requirements for the Philosophy degree can be found here.
What about a Minor?
The number of classes/hours for a minor will vary by department. Generally, some departments still require eighteen hours for the minor, while others require only fifteen hours for the minor. The Philosophy minor and the Religious Studies minor each require only fifteen (15) hours to complete.