Plants have no nervous system, so there is nothing in which experience could occur

The argument

The case against plant consciousness turns on anatomy. In every organism for which we have good reason to attribute experience, there is a nervous system: cells specialised for transmitting signals quickly over distance, gathered into structures that integrate those signals and hold them together as a single point of view. Plants have nothing of the kind. They have no neurons, no brain, no centre at which information from different parts of the organism is brought together and unified. This matters, critics argue, because consciousness is not simply the existence of responses; it is the existence of an experiencer. Pain is not the mere detection of damage but the feeling of it, and feeling requires something that the detection happens to. A plant that releases a defensive compound after being chewed has registered the damage, but there is no organ or structure in which a sufferer of that damage could be constituted. The response is distributed through tissue that has no means of assembling it into an experience. Critics add that this is not an argument from ignorance to be dissolved by future discovery. The claim is not that plant awareness has yet to be found but that plants lack the kind of architecture in which awareness is known to consist, and that no alternative architecture capable of doing the same job has been identified in them. Until such a structure is demonstrated rather than postulated, the responsible conclusion is the conservative one. Because consciousness as we understand it requires an integrating nervous system and plants possess none, this argument concludes, plants are not conscious.

Premises

Counter-arguments

Proponents of plant consciousness reply that this argument names a material rather than a function. Nerves achieve their effects by carrying and integrating signals, and plants integrate signals too, through chemical and electrical means distributed across the organism. To insist that the integration must be neural, they argue, generalises from the single case we know best instead of from any theory of what awareness requires, and simply stipulates that only brains can qualify rather than explaining why.

Rejecting the premises

[Rejecting P1] The organisms to which experience is reliably attributed are the ones we recognise, and they are recognised partly by their resemblance to us. The premise takes a feature common to the agreed cases and converts it into a requirement, which is the very inference in dispute. [Rejecting P2] That plants have no neurons and no brain is accepted; that they have no structure integrating information across the organism is a stronger claim, since vascular and chemical signalling does carry information between parts, and the premise does not say why such integration fails to count. [Rejecting P3] This is the conclusion stated as a premise. That experience requires integrating structure of the neural kind rather than widespread local response is precisely what an opponent holding that awareness comes in degrees denies.