What are the key differences between reinforcement learning and supervised learning?

Reinforcement learning (RL) and supervised learning (SL) are distinct machine learning paradigms with fundamental differences in their approaches, data requirements, and use cases. RL focuses on training agents to make sequences of decisions by interacting with an environment and learning from feedback in the form of rewards or penalties. In contrast, SL trains models using labeled datasets where each input example is paired with a known output, and the goal is to learn a mapping from inputs to outputs. The core distinction lies in how they process feedback, handle data, and optimize objectives.

In SL, the model learns from a static dataset containing input-output pairs, with explicit guidance on the correct answers. For example, an image classification model is trained on thousands of labeled images (e.g., “cat” or “dog”) to minimize prediction errors. Feedback is immediate and direct: the model adjusts its parameters based on the difference between its predictions and the ground truth labels. RL, however, operates without pre-labeled data. Instead, an agent explores an environment (e.g., a game or robot simulation) and learns by trial and error. Feedback is delayed and indirect: the agent might receive a reward only after completing a series of actions (e.g., winning a game level). For instance, an RL agent playing chess learns by evaluating moves based on eventual wins or losses, not immediate “correct/incorrect” labels.

The objectives also differ. SL aims to generalize patterns from historical data to make accurate predictions on new, similar data. It’s ideal for tasks like sentiment analysis or object detection, where clear input-output pairs exist. RL prioritizes maximizing cumulative rewards over time through strategic decision-making, making it suitable for dynamic, sequential problems like autonomous driving or inventory management. Additionally, RL requires balancing exploration (trying new actions to discover rewards) and exploitation (using known effective actions), a trade-off absent in SL. While SL models are typically trained offline on fixed datasets, RL systems often learn continuously in real-time environments, adapting to changing conditions. Both approaches have strengths, but the choice depends on the problem’s structure and the availability of labeled data.