What If a Tree Fell in a Forest and No One Hears...

This is a classic philosophical puzzle: what if a tree fell in a forest and no one hears, did the tree fall? I take this essentially as a question on existence: does something exist if it does not register on anyone's mind? The tempted answer is yes followed by the further question "but how do you know that?" The difficulty lies in the confusion of the knowledge of existence and existence itself. In physics, quantum mechanics has provided an amazing distinction between the two and I shall explicate that in a later article.

My answer is simple. The event exists, i.e. the tree fell, and if you ask how I know it, I will respond: you just told me that. My point is that the knowledge of existence requires existence whereas the converse does not hold in general or there is no way to test such condition: in the example, you have to convey that to me in the question. Because for us to know that something exists, we must observe it, i.e. in daily experience, existence and our knowledge of it are bundled together. (That explains the common confusion of the two concepts.)

P.S. Existence is a deep issue in many disciplines and it fascinates me for long. I will try to remark on it from different perspectives in the future.


  1. But how can a non-entity be the subject of a proposition? Quoting Russell, "'I think, therefore I am' is no more evident than "I am the subject of a proposition, therefore I am'". Also "the tree" in the second half of the question denotes the set of fallen trees that no one has heard, but if this set doesn't exist then "the tree" denotes a null set, making the proposition nonsensical.

    1. (are you taking the Tractatus class? if not, you should consider it. i am trying to audit but got too busy.) Yes, i agree with Russell on this point, his point (Frege gave a wonderful exposition on this) is that existential status is not an attribute of an object, i.e. if we write a statement symbolically, we cannot assert existence by "exists(the fallen tree)" but "there exists X such that X is the fallen tree."

      But as for non-existential entity can be a perfectly fine subject, e.g. "there exists X such that X is a unicorn and X is running" can be a translation of "a unicorn is running."

      So the puzzle's supposition really says this: there exists X such that X fell and no one hears. Trivially the tree fell since that is given in the supposition. I hope this will sound clear from the perspective of your comment.