Pan-Psychism is the view that nature, out there in the world and away from one's own mind, is conscious on some fundamental level. On this view apples, humans, blades of grass, and rocks might be said to be similar in at least one regard-- they are all conscious. This is not to say that a rock has the same consciousness as a blade of grass or a human being, but nonetheless there is some kind of consciousness present in them all.
To many, Pan-Psychism is absurd on the face of it. It does not seem reasonable to assume that a rock is conscious. It is reasonable to assume that other humans are conscious because the person making this very judgment in the first place would be human and see a likeness between other human beings and her or himself. There is little that is similar between a human being and a rock. In fact, one glaring similarity is that a dead, unconscious person behaves an awful lot like a rock. Therefore, inductively, rocks are like dead people. They are without consciousness. There is nothing necessarily problematic about considering that a rock might really be conscious in some limited way, but doing so is unnecessarily fanciful on the part of the asserter, as in order to do so one has to move away from any experience of the matter and into pure speculation.
This would be the conclusion to reasonably draw were there not profound problems with the alternative to Pan-Psychism. I say alternative in the singular because I know of no other alternatives that can come close to working out, or fitting with experience and science as we know it. If there are other alternatives, they need to be brought to my attention.
The alternative is that, simply put, there is conscious matter and there is unconscious matter. Within this framework, it furthermore turns out in light of chemistry that the the same basic components that assemble together to make up conscious matter also make up unconscious matter. The same elements and chemical reactions present within conscious matter can also take place, on a piece by piece basis, as unconscious matter. In otherwords, there is no chemical (no life-only chemical) that is only present in a living person and never present in a dead person or in the "unconscious" world.
Therefore, it is the unconscious bits, elements, atoms, or chemical reactions (or some combination of any or all of them) that give rise to consciousness. The details have yet to be worked out, but this does not matter. The basic ontology looks like this: there is an x such that x is unconscious and there is a y such that y is unconscious and there is an x+y, which are those very same unconscious separate components, x and y, such that x+y is conscious. A conscious state emerges when x and y come together. Separately, x and y are unconscious.
On this view there is an entity that poofs into and out of existence, namely consciousness. Whence does it come? Is there a spring of consciousness that the unconscious world connects with and, at times, invokes? Is there no spring of consciousness so that consciousness springs from nothing? Does nothing spring something? Does something blot out to nothing once more, when the y motions itself one monad more to the left of x? Does it return when the y scoots one monad back to the right?
There is one further issue that calls to be addressed--who gets to experience this conscious state? If x+y is an excruciating pain, then does x feel the pain? Does y? Do both of them feel pain as one singular perspective that sort of hovers above the two? Do none of them feel pain and a perspective, like consciousness to begin with, is invoked as if from out of an aether?
On the face of it, unconsciousness matter becoming conscious matter is something that were are used to hearing. It does not seem absurd in our culture. It is only in investigating further its implications that reveals that the position poses steep problems. Pan-psychism, on the otherhand, faces no such problems.