The Civil Code mandates that notarial wills are to be attested and subscribed by three or more credible witnesses in the presence of the testator and of one another. It is important, therefore, to determine who are qualified to become witnesses to the creation of the will. 

Under Art. 820 of the Civil Code, any person of sound mind and of the age of eighteen years or more, and not blind, deaf or dumb, and able to read and write, may be a witness to the execution of a notarial will. 

On the other hand, the disqualifications of a witness to a will is enunciated in Article 821 of the Civil Code:

Art. 821.  The following are disqualified from being witnesses to a will: 
(1)  Any person not domiciled in the Philippines; 
(2)  Those who have been convicted of falsification of a document, perjury or false testimony.

In the case of Gonzales vs CA, the Supreme Court discussed the requirements and qualifications of an attesting witness, it held that:

"Under the law, there is no mandatory requirement that the witnesses testify initially at any time during the trial as to his good standing in the community, his reputation for trustworthiness and reliability, his honesty and uprightness in order that his testimony may be believed and accepted by the trial court. It is enough that the qualifications enumerated in Article 820 of the Civil Code are complied with, such that the soundness of his mind can be shown by or deduced from his answers to the questions propounded to him, that his age (18 years or more) is shown from his appearance, testimony, or competently proved otherwise, as well as the fact that he is not blind, deaf or dumb and that he is able to read and write to the satisfaction of the court, and that he has none of the disqualifications under Article 821 of the Civil Code."

To fully understand the role of an attesting witness, the act of attestation must be differentiated from the act of subscription. In the case of Taboada vs. Rosal, the Supreme Court expounded on this difference, holding that:

"Attestation consists in witnessing the testator's execution of the will in order to see and take note mentally that those things are done which the statute requires for the execution of a will and that the signature of the testator exists as a fact. On the other hand, subscription is the signing of the witnesses' names upon the same paper for the purpose of identification of such paper as the will which was executed by the testator."

In the case of Vda.de Ramos vs. CA, the Court also discussed the nature of an attestation clause. It held that:

"Unlike other deeds, ordinary wills by necessity of law must contain an attestation clause, which is a separate memorandum or record of the facts surrounding the conduct of execution. Once signed by the attesting witnesses, it affirms that compliance with the indispensable legal formalities had been observed. The attestation clause basically contradicts the pretense of undue execution which latter on may be made by the attesting witnesses. In the attestation clause, the witnesses do not merely attest to the signature of the testatrix but also to the proper execution of the will, and their signatures following that of the testatrix show that they have in fact attested not only to the genuineness of the testatrix's signature but also to the due execution of the will as embodied in the attestation clause. By signing the will, the witnesses impliedly certified to the truth of the facts which admit to probate, including the sufficiency of the execution, the capacity of the testatrix, the absence of undue influence, and the like."

Other pertinent codal provisions regarding attestation include:

Art. 822.  If the witnesses attesting the execution of a will are competent at the time of attesting, their becoming subsequently incompetent shall not prevent the allowance of the will. 

Art. 823.  If a person attests the execution of a will, to whom or to whose spouse, or parent, or child, a devise or legacy is given by such will, such devise or legacy shall, so far only as concerns such person, or spouse, or parent, or child of such person, or any one claiming under such person or spouse, or parent, or child, be void, unless there are three other competent witnesses to such will. However, such person so attesting shall be admitted as a witness as if such devise or legacy had not been made or given. 

Art. 824.  A mere charge on the estate of the testator for the payment of debts due at the time of the testator's death does not prevent his creditors from being competent witnesses to his will.