In philosophy, constant conjunction is a relationship between two events, where one event is invariably followed by the other: if the occurrence of A is always followed by B, A and B are said to be constantly conjoined.[1] A critical philosophical question concerns the relationship between constant conjunction and causation, which has implications in the philosophy of science.
The philosopher David Hume used the phrase frequently in his discussion of the limits of empiricism to explain our ideas of causation and inference. In An Enquiry concerning Human Understanding and A Treatise of Human Nature, Hume proposed that the origin of our knowledge of necessary connections arises out of observation of the constant conjunction of certain impressions across many instances, so that causation is merely constant conjunction—after observing the constant conjunction between two events A and B for a duration of time, we become convinced that A causes B. However, this position raises problems, as it seems that certain kinds of constant conjunction are merely accidental and cannot be equated with causation. For example, we might observe sunrise following the crowing of rooster for a long period of time, but it would still be irrational to then believe the crowing causes the sunrise. Along these lines, a more modern conception would argue that scientific law is distinguishable from a principle that arises merely accidentally because of the constant conjunction of one thing and another, but there is considerable controversy over what this distinguishing feature might be.
British empiricism and associationist philosophers elaborated on Hume's fundamental idea in many diverse ways, and metaphysicians like Immanuel Kant tried to dissipate the position.[verification needed] Kant was motivated to develop his philosophy by Hume's argument, which he considered to be an attack on science.
The force of Hume's arguments has remained remarkably robust, and they have found unexpected support in three scientific discoveries of the 20th century: Ivan Pavlov's laws of conditioning; Hebbian neural networks; and spike-timing-dependent plasticity (STDP).
En el marco de Pavlov, un estímulo incondicionado puede seguir en conjunción constante a un estímulo condicionado/condicionado en un período de tiempo de milisegundos a varios segundos, y dar como resultado que el estímulo condicionado tenga muchas de las propiedades del estímulo incondicionado. Donald Hebb explicó esto como una propiedad intrínseca de los conjuntos de células dentro del sistema nervioso para formar conexiones dentro de grandes grupos de células siempre que esas células se activen juntas dentro de un período de tiempo razonablemente corto. (Una abreviatura moderna de sus ideas dice: "Las células que se activan juntas, se conectan juntas".) La neurociencia moderna ha confirmado que esta idea es un producto de la actividad de las sinapsis y el STDP, estructurado de esta manera para fortalecer las conexiones entre las células que se activan en períodos muy cortos. (decenas de milisegundos) uno del otro. Los períodos de tiempo más largos del condicionamiento clásico son presumiblemente un efecto de un gran número de camarillas de estas sinapsis y células.