# The Phi measure of integrated information is not well-defined for general physical systems

arXiv: https://arxiv.org/abs/1902.04321 · HTML: https://mlsanity.com/paper/1902.04321/

## Key facts

- Cited by 1 papers in the map (data through 14 Oct 2026).
- First posted on arXiv 12 Feb 2019.

## Built on by (most cited first, 1 of 1)

- [Toward IIT-Inspired Consciousness in LLMs: A Reward-Based Learning Framework](https://mlsanity.com/paper/2601.22786/) (2026)

## Abstract (arXiv)

According to the Integrated Information Theory of Consciousness, consciousness is a fundamental observer-independent property of physical systems, and the measure Phi of integrated information is identical to the quantity or level of consciousness. For this to be plausible, there should be no alternative formulae for Phi consistent with the axioms of IIT, and there should not be cases of Phi being ill-defined. This article presents three ways in which Phi, in its current formulation, fails to meet these standards, and discusses how this problem might be addressed.