In philosophy, causality refers to the relationship of cause and effect.

  • the cause, the correlate of the effect, is “what makes a thing do or act as it does”. This produces the effect;
  • the causality is the “current relationship of cause and effect”;
  • the principle of causality is stated as follows: “Every phenomenon has a cause”. As Spinoza writes: “Of a definite cause necessarily results an effect; and, conversely, if no definite cause is given, it is impossible for an effect to occur”. Kant states: “Law of causality: All changes happen according to the law of connection of cause and effect”.

There can be no effect without a cause. We can take as an example the appearance of life and the notion of spontaneous generation, which is an old obsolete thesis in contradiction with the principle of causality: the appearance of life necessarily has a cause. There is no counter-example to causality and it has been found in the least observation of our world. We would not be what we are without causality. His refutation would have important consequences.

A cause necessarily has an effect. We can cite the example of the second principle of thermodynamics: we can not go from one state to another without losing in the form of disorder (entropy) part of the energy that has allowed transformation. The same experiment can not be repeated indefinitely in a closed circuit (perpetual motion). Note: this postulate demonstrated by the application of statistics to the large number of molecules that compose us is observed at our scale but at the quantum level of theories speculate on non-entropic energy variations in the quantum vacuum (vacuum energy).

Plato often returns to the principle of causality. He attacks Anaxagoras, who, after having mentioned the universal Spirit, remains to the material causes, “actions of the airs, the ethers, the waters, which he invokes as causes”. Then, in Philub 27b and The sophist 254-256, he distinguishes four genera: the cause of decomposition (the Other), the mixing cause (the Same and the Rest) the unlimited (the movement), the limit (the being). In the Timaeus, he develops his thought: “We are obliged to speak of the two kinds of causes, while distinguishing between all those who are intelligent and produce beautiful and good things, and all those who, deprived of reason, produce at every turn their effects at random and without order “(46e). “Rest always resides in uniformity, and movement is a passage to the absence of uniformity, moreover the cause of the absence of uniformity is inequality” (57e). “Without necessary causes it is impossible either to apprehend the divine causes themselves, which are the only objects of our preoccupations, nor afterwards to understand them or to have any part in them” (69a).

In the Aristotelian system, the principle of causality is central. To know is to know the cause (aitia). “We think we know everything scientifically in the absolute sense when we think we know the cause of the fact that it is, that it is the cause of the thing and that it can not be otherwise than it is.”. Aristotle distinguishes four causes: the material cause (what the thing is made of), the formal cause (the essence of the thing), the motive cause (“from which there is a principle of change or rest”) , finally the final cause (what in view of what the thing is). “One calls cause, in a first sense, the immanent matter of which one thing is made: the brass is the cause of the statue … In another sense, the cause is the form and the paradigm, it is that is, the definition of quiddity; for example, for the octave, it is the ratio of 2 to 1, and, in general, the number … The cause is still the first principle of change or rest: the author of a decision is the cause of the action … The cause is also the end, that is to say the final cause. For example, health is the cause of the walk ”

Skeptics, including Sextus Empiricus, have criticized the notion of cause. “We begin to doubt the particular causal explanations, thus refuting the dogmatists who attach a great interest to it … Aenesidemus transmits to us eight modes which, according to him, are apt to manifest the vanity of any dogmatic etiology.” We can not conclude phenomena from causes, like signs to things signified, for to understand a sign we must already know the thing signified. We can only conclude phenomena to phenomena, appearances to appearances. One can only grasp their relations of succession or simultaneity in time.

The most ferocious criticism of the notion of cause comes from David Hume. We see, he says, the movement of a marble, then the movement of a second marble encountered by the first, but we do not see the active energy, the effective power, the cause that produces the movement. “All events seem entirely detached and separate. One event follows the other, but we can never see any connection between them. They seem to be linked by conjunction, but never by connection“.

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