Another new word: perturbation.
Of course I knew it existed. But one doesn't hear it very often.
I was in a small meeting in which one of the attendees, a very distinguished professor who is a specialist in the Complex Dynamic Systems Theory, at some point pointed out that one might look at anything - including for example a music lesson - as a Complex Dynamic System. All kinds of interactions are going on, and there is no way to think about what is going on in the simple terms of 'cause' and 'effect', of 'variables' which can be 'isolated'. If I understood him right - and if not, this little blog entry is completely my fault - he considered this as '19th century science'. Of which there is still a lot going on, of course.