After reading the work of David Hume, I decided – or was compelled – to test my ability to exercise independent, deliberate, original thought through my own free will. I sat still, attempted as best I could to relax my brain and mentally place myself in a starting gate, ready to spring forward with a spontaneous thought. What happened next, and happened every time I tried this exercise, was that my brain began to spin through options, like I was running my fingers through a mental rolodex.
The mental image I came up with was that the rolodex was spinning far too fast for me to see anything in detail, but as the slips flashed by I was able to sense glimpses in hindsight, like a memory of seeing what was on the slips. Some jumped out more than others, and as I remembered which ones stood out the most I looked around the room where I sat. I could either see what I remembered, or things that could easily have triggered the memory. For an example of the triggering reflex, my garage was in clear view out my back window. I associate my garage almost exclusively with mowing the lawn, since I recently moved in and my mower is just about all that I have in my garage. One of the clearest memories was of my lawn mower. Original thought seems to be the product of a trip through my mental rolodex of memories. Even inside the rolodex the memories that are on top are the most apparent, as if my brain were a chest freezer.
Bob Gregory's Gallery of Renown 