Rudolf Flesch

Rudolf Flesch (1911–1986) was an Austrian-American readability researcher and writing consultant whose work established quantitative approaches to measuring how easy text is to read.

Core ideas

• Readability formulas: Flesch developed the Flesch Reading Ease score and (with J. Peter Kincaid) the Flesch-Kincaid Grade Level — formulas that estimate text difficulty from sentence length and syllable count. These became the most widely used readability metrics in English [@flesch1949].
• Plain language advocacy: Flesch argued that public communication — government forms, legal documents, insurance policies — should be written in language ordinary people can understand. He was among the earliest advocates for what became the plain language movement.
• Conversational prose: Flesch promoted a conversational register for nonfiction: shorter sentences, common words, contractions, direct address. He treated formality as a barrier to communication, not a sign of rigor.
• Limits of formulas: Flesch’s own work acknowledged that readability formulas measure surface features (word length, sentence length), not semantic clarity. A passage can score well on readability and still be incomprehensible if it’s poorly organized or logically incoherent.

Notable works

• The Art of Readable Writing (1949)
• The Art of Plain Talk (1946)
• Why Johnny Can’t Read (1955)

Related

• readability — the concept his formulas attempted to quantify
• Janice Redish — extended plain language from readability metrics to usability testing
• plain language writing — the tradition Flesch helped establish