Do you ever catch yourself thinking some vicious little thought or surprise yourself with some smug musing?
One day we will consider the ramifications of our thoughts and words as the initiating factors of our acts and events close to us. Eventually they will be recognized as powerful elements of change in their own right. A thought can be as polluting as a deed even if we are not yet able to actually see the mess it makes. Those little black scribbles above the heads of angry cartoon characters speak to us for a good reason.
It may seem completely private and innocuous, invisible to all but ourself, and yet its having an effect more powerful than we can imagine on our subtle bodies- the ones most of us can't actually see. Its probably just as well that we can't see what that thought is doing because one day in the not so distant future we will develope the faculty and the picture won't be pretty. In the mean time we have a chance to closely observe the workings of our mind and gain some measure of control over the content!! It's called presence.
As an experiment, try repeating a string of words to yourself. You might choose negative words to begin with it you are set on making a real comparison.. I suggest you do it with uplifting words as the negative ones can actually have a devastating effect on your mood. if you are at a loss for inspiration, buy yourself a pack of angel cards or, better still, make them, and then just turn them over one by one repeating the qualities evoked on each. I find this process can turn my head space around in minutes. Its a wonderful game to do with a child aswell.
I don't believe we can actually stop the appearance of negative thoughts in our mind stream. There are many explanations for their presence. What we can do is become aware of them and turn an unconscious negative thought into a conscious positive one. It involves intention and will power. Enjoying an unpolluted psychic environment makes it worth the effort.