Short answer. You can be declared in default, and the court then proceeds to judgment without you. On the plaintiff's motion, with notice to you and proof of your failure, the court shall declare the defending party in default — after which it renders judgment granting the claimant the relief the complaint warrants.
What the law says
If the defending party fails to answer within the time allowed therefor, the court shall, upon motion of the claiming party with notice to the defending party, and proof of such failure, declare the defending party in default.
Rule 9, Section 3 — Default; [d]eclaration of. Read the full provision →
Ignoring the summons does not stall the case
The most common misunderstanding about summons is that refusing to engage keeps the case from moving. The Rules say the opposite: if you fail to answer within the time allowed, the court — on the plaintiff's motion, with notice to you and proof of the failure — shall declare you in default. Thereupon, the court shall proceed to render judgment granting the claimant such relief as his or her pleading may warrant, though it may in its discretion require the claimant to submit evidence first. The case does not wait for you; it is decided over your silence, on the other side's version of the facts.
Life as a defaulted defendant
Default does not remove you from the case — it removes your voice in it. The rule entitles a party in default to notice of subsequent proceedings, so you will know what is happening; but you may not take part in the trial. You watch, you receive orders, and you cannot cross-examine, object or present your side. The rule keeps some outer limits on the damage: the judgment cannot exceed the amount or be different in kind from that prayed for nor award unliquidated damages. But within what the complaint asked for and its facts warrant, the judgment is built without your input.
The window that closes at judgment
The Rules leave a defaulted defendant one clean way back in: a motion under oath to set aside the order of default, filed at any time after learning of it and before judgment, showing that the failure to answer was due to fraud, accident, mistake or excusable negligence and that you have a meritorious defense. Both showings are indispensable, and the deadline is unforgiving — once judgment is rendered, this remedy is gone and the road back runs through post-judgment remedies that are steeper at every step. The worst response to discovering a default order is to ignore that too.
Special cases worth knowing
Two nuances in the same rule matter. Where several defendants face a common cause of action and only some answer, the court shall try the case against all upon the answers thus filed — a co-defendant's answer can, in that scenario, keep the contest alive even for the silent one. And in actions for annulment or declaration of nullity of marriage or for legal separation, no default is allowed at all: if the defending spouse does not answer, the court orders the Solicitor General or a deputized public prosecutor to investigate possible collusion and to intervene for the State. Everywhere else, the practical advice is the same — answer on time, or see a lawyer the day you realise you have not.