Verse 9: How can I know causality is real?

asat-akaraṇāt-upādãna-grahaṇāt sarva-saṃbhavā-abhāvāt | 
śaktasya śakyakaraṇāt kāraṇa-bhāvāt-ca satkāryam ||

saṃbhava – cause (same becoming)
satkārya – the necessary existence (as inherent in a cause of an effect)

I look around (with right cognition) and find evidence of it all around me.

1. There are different kinds of indications that an effect exists in its cause.
   1. Pre-Existent Cause
      1. A tree will grow from a seed but will not grow from a grain of sand. Oil can be squeezed from a sunflower seed but not from a grain of sand.
      2. No act of production can transform something that does not already exist into existence. There is nothing I can do to extract oil from a grain of sand.
      3. Therefore I know that causality itself does not reside in the action of production but in some pre-existent cause.
      4. I can squeeze oil from the sunflower seed because its essence is already there. An entire sunflower can grow from a sunflower seed because its essence is also already there.
   2. Material Nature
      1. I select certain materials for certain effects.
      2. If I want to make yogurt I select milk, not water.
      3. This indicates that there exists a cause that has a material nature.
   3. Specificity/Fitness
      1. I cannot make gold from silver, I cannot make yogurt from water.
      2. Not all causes can produce all effects. Everything cannot produce every other thing.
      3. This indicates that there is a specific existent cause capable of producing the effect.
   4. Potential
      1. A potter can make a pot from clay earth because a potential for a pot (effect) is present in the clay (cause).
      2. A potter cannot make a pot from thread and a weaver cannot make a fabric from clay.
      3. The potter chooses the clay because a suitable effect (potential) is already present in the cause.
   5. Similarity
      1. A thread and fabric are similar – they have a shared essence. They are the same thing placed in a different order.
      2. This similarity indicates that the effect of the fabric is present in its cause, the yarn.
      3. Before production (of the fabric), cause (yarn) and effect (fabric) are identical.
      4. The present existence of an effect (curd, pot, fabric) is not a production of something new but a manifestation of a change of form.
      5. And yet, effects may possess properties that are different from their causes.
2. When I look attentively around me, I find abundant evidence that effects are present in existent causes.