How does Aristotle or a medieval scholastic commentator like St. Thomas Aquinas explain how one cause can impede the action of another cause? Or, conversely, how does the removal of an impeding cause generate an effect?

For example, consider a dam, which impedes a river's flow of water. Once a gate in the dame is opened, an impediment to the flow of water is removed, and the water gushes through. However, there is nothing in the cause (in this example: "opening a gate" or "lack of gate"*) that is in the effect (in this example: "water gushing through").
*This latter description makes it explicit that it's a privation, and privations are non-beings and thus cannot be causes; cf. De Principiis Naturæ's discussion on privation.

I'm assuming a standard description of the relation between cause and effect which St. Thomas Aquinas frequently expresses like this (Super Sent. lib. 4 d. 1 q. 1 a. 4 qc. 4 co.):

omne agens agit sibi simile, ideo effectus agentis oportet quod aliquo modo sit in agente.

Every agent effects a thing like to itself, so the effect of the agent must be in some mode in the agent.

{English translation from p. 219 of The Thomist article "The Notion of Equivocal Causality in St. Thomas" The Thomist 79 (2015):213-63.}

Clearly, the river causes is the efficient cause of the gushing water. Is the lack of a dam an instrumental cause? Are impeding causes instrumental causes?

  • 1
    Hello. Can you elaborate, give context, motivate the question? – Ram Tobolski Jan 11 '16 at 23:38
  • @RamTobolski I've very much restructured and deepened the question. I hope what I added helps clarify things. – Geremia Jan 12 '16 at 1:12
  • Just a thought; In Spinoza's "Ethics" Part Four- On Human Bondage; Axiom [page 3]. "There is no individual thing in nature, than which there is not another more powerful and strong. Whatsoever thing be given, there is something stronger whereby it can be destroyed." CMS – Charles M Saunders Jun 9 at 16:29

Taking your example: It is an aspect of the dam/gate that it is actually holding the water back. The dam is damming the water, preventing it from flowing. That is essential part of its being. Impeding itself already has the effect of impedance, it is negating something and by this has a positive effect.

Only because of that, as it is negating something, its removal can have this effect - or rather an effect different from the one that is caused by its being - at all: by ending of the effect of its being.

Thinking of the lack of a dam as causing something without ever having had any effect, i.e. without ever having been there and actually damming the river, seems to exaggerate the speech of cause and effect.


As an answer to the header question, I provide the following example:

1 - lack of food causes hunger,

2 - farming provides food,

3 - therefore farming can impede (the lack of food, which causes) hunger.


How..? By pure rhetoric: a double negation removes itself.

Don Quixote sees a peasant but he knows she is a princess made to look plain by an evil magician. Classical descriptions in terms of causes are strongly anthropomorphic and the corresponding 'explanations' are narrative constructions.

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