Article 38. The following marriages shall be void from the beginning for reasons of public policy:

(1) Between collateral blood relatives, whether legitimate or illegitimate, up to the fourth civil degree;

(2) Between step-parents and stepchildren;

(3) Between parents-in-law and children-in-law;

(4) Between the adopting parent and the adopted child;

(5) Between the surviving spouse of the adopting parent and the adopted child;

(6) Between the surviving spouse of the adopted child and the adopter;

(7) Between an adopted child and a legitimate child of the adopter;

(8) Between adopted children of the same adopter; and

(9) Between parties where one, with the intention to marry the other, killed that other person’s spouse, or his or her own spouse. (82a)


     The law speaks of void marriages by reason of public policy, as public policy frowns upon those who are closely related by blood or artificial relationship from marrying each other.

Let me give one example in regards with provision number 2 which states "between step-parents and stepchildren": 

Question: 
A woman with a child G got married to a man with a child, B. May G and B get validly married to each other?

ANSWER: Yes, because although they are considered as stepbrother and stepsister of each other, still such a marriage, while prohibited under the Civil Code, is now allowed under the Family Code.


Reference: 
Family Code of the Philippines by Albano