Power and toughness are distinct characteristics of a creature, separate from its abilities. According to CR 207.1, power and toughness are defined by the number printed in the lower-right corner of the card (or set by copy effects, characteristic-defining abilities, or counters). They are not considered "abilities" under the rules.
When an effect causes a creature to lose all abilities (for example, via an effect like Sudden Spoiling or Turn), it removes keyword abilities, activated abilities, triggered abilities, and static abilities — but it does not alter the creature's power or toughness values, because those are not abilities (CR 113.1).
There is one important exception: if a creature has a characteristic-defining ability (CDA) that sets its power and/or toughness — such as Tarmogoyf's "* /* +1" ability — losing all abilities will also cause that CDA to be lost. In that case, the creature's power/toughness would typically fall back to the printed value, or become 0 if there is no printed value (CR 604.3).
Example: Your opponent's 5/5 Gigantosaurus is targeted by Turn, which makes it lose all abilities until end of turn. Gigantosaurus has no abilities to begin with, so nothing changes functionally — it remains a 5/5 creature. Its power and toughness are completely unaffected because they are not abilities.
Unofficial fan resource — not affiliated with or endorsed by Wizards of the Coast. Answers are AI-generated estimates grounded in the Comprehensive Rules and are not a substitute for an official judge. Verify anything match-critical.