Decomposition Prompting

Decomposition prompting is the technique of instructing a language model to break a complex problem into smaller, manageable sub-problems and solve each one independently before combining the results into a final answer — leveraging divide-and-conquer logic to handle tasks that are too difficult to solve in a single reasoning step.

Why Decomposition Works

• Complex problems often involve multiple skills or knowledge areas — a single end-to-end attempt may fail because the model loses track of intermediate results or conflates different reasoning steps.
• Breaking the problem into parts lets the model focus on one aspect at a time — reducing cognitive load and improving accuracy on each sub-task.
• The compositionality of the solution mirrors how humans approach complex problems — solve pieces, then assemble.

Decomposition Prompting Methods

• Explicit Decomposition Prompt: Instruct the model to list sub-problems first, then solve each:

Break this problem into steps:
  Step 1: [identify sub-problem]
  Step 2: [identify sub-problem]
  ...
  Now solve each step:
  Step 1 solution: ...
  Step 2 solution: ...
  Final answer: [combine]

- Least-to-Most Prompting: A specific decomposition framework:
1. Decomposition Stage: "What sub-problems do I need to solve to answer this?"
2. Solution Stage: Solve sub-problems from simplest to most complex, with each solution available for subsequent sub-problems.
- Key insight: Later sub-problems can reference earlier solutions — building up to the final answer incrementally.

• Recursive Decomposition: Each sub-problem can itself be decomposed further if still too complex — creating a tree of sub-problems.

Decomposition vs. Chain-of-Thought

• CoT: Linear sequence of reasoning steps — one continuous narrative from problem to answer.
• Decomposition: Hierarchical — first identify the structure of the problem, then solve components, then combine.
• Decomposition is more effective for problems with independent sub-components that can be solved separately.
• CoT is more natural for problems with sequential dependencies where each step directly feeds the next.

When to Use Decomposition

• Multi-Part Questions: "Compare X and Y across dimensions A, B, and C" — decompose into separate comparisons.
• Complex Math: Multi-step word problems — decompose into individual calculations.
• Research Questions: "What are the implications of X?" — decompose into economic, social, technical implications.
• Code Generation: Complex functions — decompose into helper functions, then compose.
• Long Documents: Summarize or analyze by section, then synthesize.

Benefits

• Accuracy: Decomposition improves accuracy by 10–25% on complex reasoning tasks compared to direct answering.
• Transparency: Each sub-problem and its solution is visible — easy to identify where errors occur.
• Scalability: Handles arbitrarily complex problems by recursive decomposition — complexity is managed, not avoided.

Decomposition prompting is one of the most effective techniques for complex reasoning — it transforms overwhelming problems into tractable pieces, reflecting the fundamental computer science principle that hard problems become easy when properly decomposed.