Shape is morphology without an internal state and a source term. That is the ice neuron.
Excitability adds active cable.
Field closure is the biophysical mélange in which the neuron writes part of the field that then acts back on it. That is the biological neuron.
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The Silhouette Fallacy: Field closure, ephaptic coupling, and the physics of computation
Companion post to: Field closure, ice neurons, and when a dendrite is a motif Nima Dehghani arXiv 2026 DOI: https://arxiv.org/abs/2610.00184v1