To explore a little more deeply what is meant by the Imaginary Nature of Existence, let’s begin with Khenpo Tsultrim Gyamtso Rinpoche’s definition:
The imaginary nature exists as mere conceptual creations. It is the objects that our concepts and ideas refer to. For example, since the real tiger in a dream is non-existent, it is merely a figment of the imagination. In other words, the imaginary nature, which refers to the contents of the delusion rather than the delusion itself, exists only in the imagination as the referent of names and concepts. For example we talk about past events. These events do not exist at all. They are simply names or concepts for referring to things that are being imagined, but which do not exist. Objects external to the mind and senses are of this nature. They do not exist and yet names and concepts are applied to them.
So, to reiterate, the imaginary nature “refers to the contents of the delusion rather than the delusion itself.” When we’re dreaming of a tiger, the dream-tiger, as a dream -- i.e. as a projection of our mind -- has a certain kind of “existence” or “reality” that cannot be denied. In other words, the delusion itself, the dream itself, is indeed appearing. But the supposed content of the dream/delusion -- namely an objectively-existing tiger -- has no real existence, but rather is simply imaginary: a fact we become aware of, when we wake up in our bedroom, and notice that there is no tiger to be found, anywhere.
Tai Situ Rinpoche explains the Imaginary Nature in a similar way:
... the imaginary aspect of experience refers to what our thoughts are thinking about, what our thoughts are projecting. These are just conceptual creations, they have no existence and don’t appear anywhere in the world. This includes all the names that we give to things and it is pretty easy to understand.
In relation to the practice of naming things, he explains:
An imaginary nature is something that is only a projection of mind. For example, we call the things we put our feet in “shoes.” We could call them hat or jacket but in the beginning the English people decided to call them shoes. Tibetans call them lham and in India we use the Hindi word jut. These labels are all kuntag, imaginary natures.
The very process of “naming” involves an abstraction from direct experience, from the flowing interconnected luminous weave of Reality. It involves the creation of more-or-less arbitrary conceptual boundaries, whose “existence” is only of the Imaginary Nature.
Shantarakshita expands a bit on this naming process, by including in his discussion the “signs” i.e. the characteristics according to which we designate/name the “things” of our conceptual universe:
... the word “sign” refers to what appears as the characteristics of shape, solidity, and so forth (as in the case of an object like a vase). When the name “vase” is attached to the characteristics of a vase, the characteristics of all other things are implicitly excluded, and the label is identified with the vase itself. This is what is meant by a name. By giving a name to something, one gives a clear indication of what the characteristics (i.e., the sign) of the thing are. These two items (sign and name) constitute imputed nature (kun btags) because they are the domain of words and thoughts in being the dualistic appearance of subject and object, which, when investigated, are found to be false or deceptive.
So, once again, included in the Imaginary Nature or Aspect of Experience are (1) names -- linguistic/conceptual categories; and (2) the supposed “objects” that our mental thoughts and images refer to. Because we have collectively created the name “Santa Claus” and “unicorn,” for instance, I can easily create a mental image of Santa Claus, or a mental image of a unicorn -- but if I traveled to the North Pole looking for the “real” Santa Claus, or for a “real” unicorn, I would never find them as anything other than mental projections. They are only imaginary.
It’s the same with past events: while I can conjure a “memory” of a past event, the event itself is nowhere to be found, other than in my mind, as a mental projection. As such, past events -- like dream-tigers and Santa Claus and unicorns -- belong to the Imaginary Nature.
The most problematic of all imaginary creations is that of a separate, inherent and unchanging “self.” The assumption of a truly-existent separate “me” is the cause of all our suffering.