When can you use an alias legally?

An alias by the way is a false or assumed identity.

A Filipino citizen residing in this country can use an alias legally in the  following instances:
1. Pseudonym for literary purposes
2. Use of aliases in cinema and television entertainment
3. In athletics and sports activities (RA 6085)
4. Under the witness protection program, a person may adopt a different identity (RA 6931)
5. When he has been baptized or customarily known by such alias
6. When authorized by a competent court (CA. No.142, as amended by RA. 6985).
7. When properly indicated in a certificate of candidacy (Omnibus Election Code)

Read: Anti-Alias Law (C.A. No.142)