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Conditioned Co-production : the idea central to Buddhism that all things occur in dependence on conditions, and when those conditions cease, things cease - their existence being relative.

pratityasamutpada

 "This being, that becomes,
From the arising of this, that arises,
This not becoming, that does not become
From the ceasing of this, that ceases"
Majjhima-Nikaya II.32.
Samyutta-Nikaya, II.28

The realisation that all things change is one of the key insight experiences that the Buddha had; that all things are impermanent.  For Buddhists, the important thing is not to just understand that all things are impermanent, but to live your life in this way, and experience the world as impermanent.  This is what Buddhist call wisdom.  The Buddhist word for wisdom is "Prajna". 
 
The other key insight that the
Buddha had was that all things are conditioned.  The idea that all things are conditioned is sometimes called the doctrine of pratityasamutpada or Conditioned Co-production.  The outer rim of the Bhavachakra represents the functioning of Conditioned Co-production (J-U).  It says that all things come about because of a set of conditions that are in place.  If the conditions are not in place then that event or state of affairs will not arise. This was what the Buddha discovered in his experience of Enlightenment.

The best way to understand the notion of Conditioning is to think of a plant.  A plant starts off as a seed, but if there is not any soil, any sun, and any rain, the seed will not grow.  If there are not the right conditions, then the seed will now germinate and grow into a beautiful plant.  The seed, the water, the heat and the nutrients in the soil are the conditions that the fully-grown plant depends upon.  If those conditions are not in place, the plant will not arise.
 
In a more practical and down to earth sense it means that we don't live on this earth for very long, and that human life is fragile and precious, so we better get on with it, and not waste our time; not waste this precious life in laziness or being unhappy, or moaning about things. Just get on with life!

Fig 28 

Karma & The Twelve Links

Because everything is always changing of this, we are not a THING at all, but are a process of change.  Buddhism shows how this process of change happens.  The outer rim of the Wheel of Life explains the workings of Conditioned Co-production.  This is a complicated way of saying that all things change as a result of previous states of affairs, or conditions.   This conditioning also includes us.  The idea of things being conditioned is represented in twelve pictures or links, called the Twelve Nidanas.
 
Our actions, and our states of mind, effect what happens to us in the future, effect what we become in future.  The important
Buddhist word Karma used to describe "willed" or deliberate action.  Karma is related to Karma-Vipaka, which is the "fruit" of the willed action.  The idea is that when we act it is as if we put down seeds, good or bad seeds.  These seeds, if the conditions are right, might ripen in the future, and we will therefore experience the consequences of our previous actions.  We will literally reap what we so.
 
Another way to think of
Karma is the idea that actions have consequences.  If you have a important football match coming up, and you decide to spend the time between then and now, going out, getting drunk, staying up late, not going to any practices and generally not preparing, then you can not expect to do very well on match day.  Another example is school, if you spend two years not concentrating in class, not doing any work, not doing your homework or coursework, then you can't really expect to pass you exams.  Your actions, and your lack of actions too, have consequences.

Skillfulness & Unskillfulness          

Buddhism says that our actions are good or bad depending on our intentions, or the state of mind that we are in when we act.  We can act in a skillful way, that is with an intention of love and compassion and understanding and awareness, or from an unskillful way, with an intention based in greed, ignorance and hatred.  If we act in a hateful way we tend to create bad or hateful effects, if we act in a calm and kind way, we tend to produce calm and kind effects. 
 

Buddhism says that how we live our life affects what we become in the future.  If we do lots of actions that are based on being cruel and unkind, then this is the sort of person that we become, if we try to be kind and giving, then this is the sort of person that we become.  One way of thinking about this is that we are, if you like, a habit.  Habits have a tendency to grow, to become more "habitual".  What we give attention to becomes more formed and stronger.  The more habits are indulged in, the more difficult they are to change.  The trick is to make sure that we are a good habit. 
 
Sometimes positive change or development is really hard and you seem to be getting nowhere.  The Buddha said that this is a bit like someone trying to smash a rock with a hammer.  You can keep on hitting and hitting it, but you may never seem to get anywhere; but on the last blow, it splits.  The question is, which blow caused the rock to break, the last one?  No, it was all of the blows that split the rock.