Internal reconstruction is a method used by linguists to study the historical development of a language. It involves analyzing variations within a single language to infer how its sounds, grammar, or vocabulary may have changed over time. By examining irregular forms or patterns, researchers can reconstruct earlier stages of the language. This technique is particularly useful when there are no written records available, allowing linguists to make educated guesses about the language's evolution. Internal reconstruction can reveal insights about related languages, such as Proto-Indo-European, and help understand the relationships between different language families.