In philosophy, which qualities define the identity of an object?

The correct answer is essential qualities because, in philosophy, essential qualities are those characteristics that are necessary for an object to be what it is. These qualities define the fundamental nature of the object and determine its identity. For instance, the essential qualities of a triangle include having three sides and three angles; without these traits, it would not be a triangle.

Essential qualities contrast with particular qualities, which may refer to characteristics that can vary without changing the object's fundamental identity. Secondary qualities pertain to perceptions, such as color or taste, which do not inherently belong to the object but are experienced by observers. Primary qualities, on the other hand, refer to measurable attributes like shape, size, and motion, which can be objectively observed and quantified, yet they do not encompass the essence of the object itself.

In summary, essential qualities encapsulate what fundamentally constitutes the identity of an object, making it the most accurate choice in the context of philosophy.