A Problem in Philosophy

They say my room does not exist
  Except when I am there.
This vague and shadowy state of things
  Is more than I can bear.
I'll test the truth of it myself;
  I'll catch it unaware.

With books piled high, I'll make believe
  I'm going out to stay;
I'll say quite loud, "I'll not return
  Till later in the day,"
And give it, oh, a splendid chance
  To vanish quite away.

Then softly will I creep around
  Beneath my window high;
And with a ladder tall and strong
  I'll climb so still and sly.
I'll look - and prove that theory
  And find if it's a lie.

- Alice M. Watts, 1909.