over and thought of. Terms similar to the broad notion of object include thing, being, entity, item, existent, term, unit, and individual. In ordinary language, one is inclined to call only a material object "object". In certain contexts, it may be socially inappropriate to apply the word object to animate beings, especially to human beings, while the words entity and being are more acceptable. Some authors use object in contrast to property; that is to say, an object is an entity that is not a property. Objects differ from properties in that objects cannot be referred to by predicates. Such usage may exclude abstracts objects from counting as objects. Terms similar to such usage of object include substance, individual, and particular. The word object can be used in contrast to subject as well. There are two definitions. The first definition holds that an object is an entity that fails to experience and that is not conscious. The second definition holds that an object is an entity experienced. The second definition differs from the first one in that the second definition allows for a subject to be an object at the same time. Change An attribute of an object is called a property if it can be experienced (e.g. its color, size, weight, smell, taste, and location). Objects manifest themselves through their properties. These manifestations seem to change in a regular and unified way, suggesting that something underlies the properties. The change problem asks what that underlying thing is. According to substance theory, the answer is a substance, that which stands for the change. Problem of substance Because substances are only experienced through their properties a substance itself is never directly experienced. The problem of substance asks on what basis can one conclude the existence of a substance that cannot be seen or scientifically verified. According to David Hume's bundle theory, the answer is none; thus an object is merely its properties. In the Mūlamadhyamakakārikā Nagarjuna seizes the dichotomy between objects as collections of properties or as separate from those properties to demonstrate that both assertions fall apart under analysis. By uncovering this paradox he then provides a solution (pratītyasamutpāda – "dependent origination") that lies at the very root of Buddhist praxis. Although Pratītyasamutpāda is normally limited to caused objects, Nagarjuna extends his argument to objects in general by differentiating two distinct ideas – dependent designation and dependent origination. He proposes