…our Homo sapiens ancestors: their newly acquired causal imagination enabled them to do many things more efficiently through a tricky process we call “planning.” Imagine a tribe preparing for a mammoth hunt. What would it take for them to succeed? My mammoth-hunting skills are rusty, I must admit, but as a student of thinking machines, I have learned one thing: a thinking entity (computer, caveman, or professor) can only accomplish a task of such magnitude by planning in advance – by deciding how many hunters to recruit; by gauging, given wind conditions, the direction from which to approach the mammoth; in short, by imagining and comparing the consequences of several hunting strategies. To do this, the thinking entity must possess, consult, and manipulate a mental model of its reality.

– Pearl and Mackenzie [2018, p. 25]

Deterministic planning is the process of finding a sequence of actions to achieve a goal. Because an agent does not usually achieve its goals in one step, what it should do at any time depends on what it will do in the future. What it will do in the future depends on the state it is in, which, in turn, depends on what it has done in the past. This chapter presents representations of actions and their effects, and some offline algorithms for an agent to find a plan to achieve its goals from a given state.

This chapter makes the following simplifying assumptions:

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  There is a single agent.

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  The agent’s actions are deterministic and the agent can predict the consequences of its actions.

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  There are no exogenous events beyond the control of the agent that change the state of the environment.

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  The environment is fully observable; thus, the agent can observe the current state of the environment.

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  Time progresses discretely from one state to the next.

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  Goals are predicates of states that must be achieved.

Some of these assumptions are relaxed in the following chapters.