AI

Understanding Reasoning in AI: Fast and Slow

How dual-process thinking maps to AI systems, when to use fast heuristics versus slow, deliberate reasoning, and why Indian languages are essential for reliable AI in India.

Indhic Research Team
August 14, 2025
9 min read
ReasoningCognitive ScienceAIIndiaLanguage Technology
Understanding Reasoning in AI: Fast and Slow
In this post, we'll dive into how AI mimics our "fast and slow" thinking, why it matters, and crucially why ignoring India's linguistic tapestry could make your AI system as unreliable as a monsoon forecast gone wrong.
"The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge." - Stephen Hawking

The Two Sides of the AI Mind: Your Brain's Blueprint

Nobel laureate Daniel Kahneman nailed it with his dual-process theory: We've got System 1 (the speedy, gut-feel autopilot that spots a snake in the grass without breaking a sweat) and System 2 (the thoughtful analyst that puzzles over a crossword or debates a life decision). It's like the difference between snapping a selfie and composing a masterpiece painting.
AI is evolving to mirror this split. Picture a chatbot: It might fire off a quick recipe based on patterns it's seen a million times (fast mode). But for thorny problems, like debugging code or verifying facts, it needs to slow down, plot steps, and even call in reinforcements like tools or searches.

The art of building killer AI?

Knowing when to hit the gas and when to pump the brakes. Get it wrong, and your AI becomes that overconfident friend who always has an answer but rarely the right one.
Daniel Kahneman's dual-process theory describes two complementary modes of human thought:
System 1 (fast): Quick, automatic, intuitive judgments that require little effort
System 2 (slow): Deliberate, logical, and effortful reasoning that consumes more energy
Modern AI systems are moving towards such splits. Some behaviors are fast, pattern-based responses while others require explicit reasoning steps, search, or tool use.
Designing useful AI systems often means knowing when to rely on fast heuristics and when to engage slow, step-by-step thinking and marry the both to produce a system that is useful while balancing the constraints and tradeoffs.

What "Reasoning" Actually Means in Generative AI

In Gen-AI, reasoning is the ability to form intermediate steps that connect a question to a reliable answer. Concretely, systems can:
Plan → Outline steps before attempting a solution
Decompose → Break a problem into subproblems and solve them sequentially
Search → Explore alternatives (beam search, tree-of-thought, self-consistency)
Use tools → Call calculators, code interpreters, search engines, or domain APIs
Verify → Check results against constraints, evidence, or tests
"The best AI doesn't just give you an answer—it shows you how it got there."
Fast pattern matching is powerful for familiar tasks and style transfer. Slow reasoning is essential when facts are uncertain, steps must be justified, or errors are costly.

Fast vs. Slow: Real-World Battle

Math word problems • Fast: Produce a plausible number by pattern matching • Slow: Write intermediate equations, compute, and verify units and constraints
Coding and debugging • Fast: Suggest a fix based on similar snippets • Slow: Run tests, inspect stack traces, isolate the failing case, and retry
Knowledge questions • Fast: Retrieve a familiar fact • Slow: Retrieve sources, cross-check dates and names, and cite evidence
The slow path often looks like: plan → solve → check → revise. Systems that externalize these steps are more transparent and easier to trust.
"Trust is built step by step literally by ensuring well curated evaluations and measuring the ROI."

Making AI Think Before It Speaks

You can encourage deliberate reasoning with lightweight techniques:
Prompt for steps → Use phrases like "let's reason step by step" or "first list assumptions, then solve, then verify"
Self-consistency → Sample multiple solutions and pick the majority or the best-scoring one
Decomposition → Ask for a plan before execution; solve subparts individually
Tool use → Route arithmetic to a calculator, code to a runner, search to a retriever
Guardrails → Require a final check against constraints (totals must sum, dates must match sources)
These strategies raise reliability without retraining the underlying model.

Why Language is the Secret Sauce of Reasoning

Reasoning is expressed through language: naming assumptions, defining terms, and chaining steps. Models that understand linguistic nuance (negation, quantifiers, modality, discourse markers) produce clearer intermediate steps and fewer logical slips.
Ambiguity in natural language (pronouns, ellipses, idioms) is a major source of reasoning errors. Clear prompts and structured intermediate representations (lists, tables, JSON) reduce that ambiguity and improve step-by-step correctness.

The Indian Languages Challenge: Why One Size Doesn't Fit All

Building reliable AI for India requires attention to linguistic reality:
Diversity → India has 22 scheduled languages and hundreds of other languages and dialects across different language families
Scripts and orthography → Devanagari, Bengali-Assamese, Gurmukhi, Gujarati, Oriya, Tamil, Telugu, Kannada, Malayalam, and more, each with unique normalization, tokenization, and rendering needs
Morphology and syntax → Many Indian languages are morphologically rich and permit flexible word order, which can obscure roles like who-did-what without good parsing
Code-mixing and transliteration → Hinglish, Tanglish, and other blends are common, often written in Latin script. Reasoning can fail if the model can't align mixed or transliterated text to native-script knowledge
Domain vocabulary → Government, finance, agriculture, healthcare, and law use specialized terms in multiple languages that must be translated consistently
"An AI that 'reasons' well in English may not transfer that reliability to Indian languages unless it is grounded in high-quality, language-specific data and evaluation."
Linguistic reality in India: diversity, scripts, morphology, code-mixing, domain vocabulary

Linguistic reality in India: diversity, scripts, morphology, code-mixing, domain vocabulary

Your India-Ready AI Playbook

Data coverage → Curate balanced corpora across major Indian languages, including colloquial, code-mixed, and transliterated text. Leverage open initiatives where appropriate and supplement with domain data
Script support → Implement Unicode-aware normalization, grapheme-safe tokenization, and robust font/rendering pipelines for each script you target
Transliteration bridges → Support round-trip transliteration (Latin ↔ native scripts) so mixed-script inputs still map to the same meaning and knowledge
Evaluation → Use multilingual benchmarks and create task-specific tests (government form understanding in Hindi, crop-advisory Q&A in Tamil). Include step-by-step scoring, not just final answers
Tooling and UX → Prefer structured outputs (lists, tables) for intermediate steps; add calculators, retrieval, and code runners as first-class tools. Offer voice input and TTS where literacy or accessibility demands it
Safety and context → Tune for culturally relevant norms, local regulations, and harmful-content policies in each language
"Building for India isn't just translation — it's transformation."

The Speed vs. Accuracy Dilemma: When to Choose What

Use fast for: Routine classification, style transformations, summaries of well-known topics, familiar customer queries
Use slow for: Financial or legal advice, healthcare triage, multi-hop factual questions, data transformations with strict constraints, any action that triggers irreversible changes
"Speed kills—but so does being too slow. The art is knowing which one matters more."
A pragmatic pattern is a two-stage system: fast first-pass to draft, slow second-pass to check, correct, and cite.

Seeing It in Action: A Simple Example

Question: A co-operative buys 3 fertilizer sacks at ₹740 each and gets a ₹120 bulk discount. What is the total?
Fast guess: 3 × 740 = 2220 • Slow steps: 3 × 740 = 2220 → 2220 − 120 = 2100. Answer: ₹2100
Even simple arithmetic benefits from explicit steps; the gap grows on multi-hop or code-mixed queries.
"The difference between right and wrong is often just one missing step."

The Bottom Line: Building AI That Actually Works

Designing AI that truly "reasons" means optimizing both minds: the fast one for efficiency and the slow one for trust.
"The future belongs to AI that can think fast when it needs to, and slow when it matters and reproduce the human brain's complex logical reasoning abilities in an efficient way"

Key Takeaways

• Reasoning quality depends on explicit intermediate steps and verification, not just model size
• Language is the medium of reasoning; support for Indian languages (scripts, code-mixing, and domain terms) is essential for reliability in India
• Combine fast heuristics with slow, deliberate pipelines and the right tools to balance speed and accuracy

Lessons from the Indhic Trenches

• Add step-by-step prompting and final verification checks to critical workflows
• Integrate tool use for calculation, retrieval, and evaluation where appropriate
• Build multilingual evaluation with step-level scoring across key Indian languages
• Implement Unicode normalization, grapheme-safe tokenization, and transliteration bridges in your stack
• Pilot a two-stage fast (non-reasoning)/slow (reasoning) pipeline on a production task
• Leverage LLM judges against different LLM responses to measure accuracy and latency
Written by Indhic Research Team
Published on August 14, 2025