If there is a baby suffering from loose motions, we can say that the cause of the loose motions is probably an infection.
we find that the infection came through unclean drinking water. But many babies must have had this unclean drinking water. So, why is it that one
baby developed loose motions when the other babies did not?
One reason might be that this baby is not healthy. As a result, it might be more likely to have disease when exposed to risk, whereas healthier babies would not. Why is the baby not healthy? Perhaps because it is not well nourished and does not get enough food. So, lack of good nourishment becomes a second cause of the disease. Further, why is the baby not well nourished? Perhaps because it is from a household which is poor.
It is also possible that the baby has some genetic difference that makes it more likely to suffer from loose motions when exposed to a pathogen. Without the pathogen, the genetic difference or the poor nourishment alone would not lead to loose motions. But they do become contributory causes of the disease.
Why was there no clean drinking water for the baby? Perhaps because the public services are poor where the baby’s family lives. So, poverty or lack of public services become third cause of the baby’s disease.
It will now be obvious that all diseases will have immediate causes and contributory causes. Also, most diseases will have many causes, rather than one single cause.