What is the error in the quote: "In order to study all night for her test?"

The primary issue with the quote "In order to study all night for her test?" stems from its structure, specifically in how it conveys its purpose. The phrase “In order to” introduces an intention or purpose, which should follow with a complete sentence that explains what the subject intends to do. In this case, although “her” may seem problematic, the real concern lies in the lack of a main clause that clarifies the purpose of studying all night.

To correct the structure, a complete thought should be provided. For example, one could say, "In order to study all night for her test, she prepared her materials." This structure offers both the intention and the action taken to fulfill that intention.

The other elements of the quote—“In order to,” “for,” and “test?”—either function properly within the context of a complete sentence or don’t impact the grammatical integrity as fundamentally as the unfulfilled promise of a main clause does in this case.