Internal Reconstruction

Irregularities often mark places where regular sound change has disrupted an older, regular pattern. For example, if a verb conjugation shows a regular pattern in most forms but exceptions in others, the exceptions often preserve the effects of an old sound change that has since become opaque. By reverse-engineering what the original system must have been, linguists infer historical states.

Suppletion occurs when an inflected form comes from an entirely different root (e.g., English 'go/went'). Suppletion often indicates historical merger of two verbs or survival of archaic forms. Irregular morphology, by contrast, is a departure from productive patterns (e.g., 'deer/deer' plural is irregular compared to the regular '-s' pluralization). Both can signal historical change, but suppletion is more dramatic evidence of historical borrowing or merger.

Internal Reconstruction can establish the relative sequence of sound changes—which happened before which—through morphological evidence. However, it cannot date changes in absolute terms (e.g., how many centuries ago). For absolute dating, you need external anchors like written records, archaeological context, or glottochronological estimates.

Conflicts are rare if both methods are applied carefully. When they occur, the Comparative Method usually takes precedence because it has multiple independent witnesses (related languages), whereas Internal Reconstruction relies on a single language's patterns. However, the conflict may signal errors in data collection or analysis, and investigating the discrepancy often yields insights.