Degree certificates are provided by the University's Degree Conferrals office, rather than by Somerville. They are automatically issued following graduation whether you have graduated in person or in absence. You must have graduated at a degree ceremony (either in person or in absence) in order to obtain a degree certificate.
If you have lost your original degree certificate you can order a replacement from the University's Degree Certificates Web page.
If you have not yet graduated but need proof that you have completed your degree, you can order a Degree Confirmation statement via the Web site above.