Counterfactual planning is a design approach for creating a range of safety mechanisms that can be applied in hypothetical future AI systems which have Artificial General Intelligence.
My new paper Counterfactual Planning in AGI Systems introduces this design approach in full. It also constructs several example AGI safety mechanisms.
The key step in counterfactual planning is to use an AGI machine learning system to construct a counterfactual world model, designed to be different from the real world the system is in. A counterfactual planning agent determines the action that best maximizes expected utility in this counterfactual planning world, and then performs the same action in the real world.
Examples of AGI safety mechanisms that can be constructed using counterfactual planning are:
An agent emergency stop button, where the agent does not have a direct incentive to prevent its stop button from being pressed
A safety interlock that will automatically stop the agent before it undergoes an intelligence explosion
An input terminal that can be used by humans to iteratively improve the agent's reward function while it runs, where the agent does not have a direct incentive to manipulate this improvement process
A counterfactual oracle.
Counterfactual planning is not a silver bullet that can solve all AI alignment problems. While it is a technique for suppressing strong direct incentives, it will not automatically remove all remaining indirect incentives which can also lead to unsafe behavior.
In this sequence of Alignment Forum posts. I will give a high-level introduction to counterfactual planning. The sequence uses text and figures from the paper, but omits most of the detailed mathematical definitions in the paper.
I have also added some extra text not included in the paper, observations targeted specifically at long-time LessWrong/Alignment Forum readers. For example, in LessWrong terminology, the paper covers subjects like agent foundations, decision theory, and the embedded agency, but you won't find these terms being mentioned in the paper.
Use of natural and mathematical language
When writing about AGI systems, one can use either natural language, mathematical notation, or a combination of both. A natural language-only text has the advantage of being accessible to a larger audience. Books like Superintelligence and Human Compatible avoid the use of mathematical notation in the main text, while making a clear an convincing case for the existence of specific existential risks from AGI, even though these risks are currently difficult to quantify.
However, natural language has several shortcomings when it is used to explore and define specific technical solutions for managing AGI risks. One particular problem is that it lacks the means to accurately express the complex types of self-referencing and indirect representation that can be present inside online machine learning agents and their safety components.
To solve this problem, counterfactual planning introduces a compact graphical notation. This notation unambiguously represents these internal details by using two diagrams: a learning world diagram and a planning world diagram.
AGI safety as a policy problem
Long-term AGI safety is not just a technical problem, but also a policy problem. While technical progress on safety can sometimes be made by leveraging a type of mathematics that is only accessible to handful of specialists, policy progress typically requires the use of more accessible language. Policy discussions can move faster, and produce better and more equitable outcomes, when the description of a proposal and its limitations can be made more accessible to all stakeholder groups.
One aim of the paper is therefore to develop a comprehensive vocabulary for describing certain AGI safety solutions, a vocabulary that is as accessible as possible. However, the vocabulary still has too much mathematical notation to be accessible to all members of any possible stakeholder group. So the underlying assumption is that each stakeholder group will have access to a certain basic level of technical expertise.
At several points in the paper, I have also included comments that aim to explain and demystify the vocabulary and concerns of some specific AGI related sub-fields in mathematics, technology, and philosophy.
On this forum and in several AI alignment/safety agendas, it is common to see calls for more work on agent foundations.
Counterfactual planning can be read as a work on agent foundations: it offers a new framework for understanding and reasoning about agents. It provides a specific vantage point on the internal construction of machine learning based agents. This vantage point was designed to make certain safety problems and solutions more tractable.
At the same time, counterfactual planning takes a design stance. It does not try to understand or model all possible forms of agency, for example it is not concerned with modeling agent-like behavior in humans or organizations. The main interest is in clarifying how we can design artificial agents that have certain safety properties.
In the machine learning community, it is common to use agent models where the agent is as a mechanism designed to approximate a certain function as well as possible. The agent model in counterfactual planning also treats machine learning as a function approximation, but it constructs the agent by building additional moving parts around the function approximation system. By re-arranging these moving parts, compared to the standard configuration that is implicitly assumed in most agent models, we can create a counterfactual planner.
This re-arrangement can also be interpreted as constructing an agent that will use a customized decision theory, a decision theory that is explicitly constructed to be flawed, because it will make the agent ignore certain facts about the environment it is in.
MIRI's discussion of decision theory puts a strong emphasis on the problem an agent's machine reasoning system may get deeply confused and possibly dangerous when it does the wrong type of self-referential reasoning. The solution to this problem seems obvious to me: don't build agents that do the wrong type of self-referential reasoning! So a lot of the paper is about describing and designing complex forms of self-referencing.
The paper (and this sequence) breaks with the LessWrong/Alignment Forum mainstream, in that I have consciously avoided using the terminology and examples of self-referential reasoning failure most frequently used on this forum. Instead, I have aimed to frame everything in the terminology of mainstream computer science and machine learning. To readers of this forum, I hope that this will make it more visible that mainstream academia has also been working on these problems too, using a different terminology.
In some parts of the mainstream machine learning community, counterfactuals have been routinely used to improve the performance of the machine learning system, for example in poker, see this paper from 2007 and in computational advertizing, see this paper from 2013.
In the computational fairness community counterfactuals have been proposed as a way to define and compute fair decisions, in this key 2017 paper. In the fairness community, there is also significant discussion about how easy or difficult it may be to compute such counterfactuals see this recent book chapter for an overview.
In both cases above, the counterfactuals being constructed are Pearl's counterfactuals based on Causal Models, as defined by Pearl around 2000. I'd say that the use of Pearl's system of counterfactuals is the de-facto standard in the mainstream machine learning community.
However, in the AGI safety/alignment community, in particular in the part of the community represented here on the Alignment Forum, the status of Pearl's causal models and counterfactuals is much more complicated.
The 2015 MIRI/FHI paper Corrigibility identified counterfactual reasoning as a possible solution direction for creating AGI agent stop buttons. Counterfactual reasoning is an open problem on MIRI's 2015 technical research agenda. But much of the work on counterfactual reasoning which has been posted here has not engaged directly with Pearl's work. The impression I have is that, since 2015, several posters have been trying to define or clarify notions of counterfactuals which are explicitly different from Pearl's system. These attempts have often used Bayesian updates as a building blocks. This work on non-Pearlian counterfactuals has lead to interesting but also sometimes confusing discussions and comment threads, see for example here.
One partial explanation for this state of affairs may be that MIRI's approach to alignment research is to take high-risk bets on developing completely novel breakthroughs. They prefer to look for solutions in places where the more mainstream academic and machine learning communities are not looking.
There is also the factor that Pearl's work is somewhat inaccessible. Pearl's presentation of his mathematical system, both in his papers and in the book Causality, seems to have been written mainly for an audience of professional statisticians, for example statisticians working in the medical field. The presentation is not very accessible to a more general technical audience. Pearl and Mackenzie's The Book of Why is more accessible, but at the cost of omitting the mathematical foundations of the notation.
Nevertheless, in my experience, Pearl's mathematical system of causal models and counterfactuals is both powerful and useful. So I have built on this somewhat mainstream system to define counterfactual planning in machine learning agents.
But in the paper I have departed from Pearl's work by defining his mathematical counterfactuals from scratch, in a way that explicitly avoids the use of Pearl's framing, justifications, and explanations. I depart from Pearl's framing by using the notion of mathematically constructed world models as a central organizing theme.
I am also building on recent work by Tom Everitt and others, who have been promoting the use of Pearl causal models, and their graphical representation as Causal Influence Diagrams, in the AGI safety community.
Everitt et al. present Causal Influence Diagrams primarily as an analytical device, to explore the incentives of an agent. I have gone one step further, and use the diagrams as a device to fully define entire agents. This turns the diagrams into design tools. In section 8 of the paper I show a design process that creates indifference by redrawing the agent's planning world diagram.