These results showed the importance of readability for unassisted reading where pressure to complete a course of study is low and competition from distractions is high.

The measurement of content

For hundreds of years, writers and teachers have used and taught the cognitive and structural factors in text such as organization and coherence. Researchers in readability also addressed the effects of these factors on comprehension:
  • Image words, abstraction, predication, direct and indirect discourse, types of narration, and types of sentences, phrases, and clauses (Gray and Leary 1935).
  • Difficult concepts (Morriss and Holverson 1938, Chall 1958).
  • Idea density (Dolch 1939).
  • Human interest (Flesch 1949, Gunning 1952)
  • Organization (Gunning 1952, Klare and Buck 1954, Chall 1958).
  • Nominalization (Coleman and Blumenfeld 1963; Coleman, 1964)
  • Active and passive voice (Gough 1965, Coleman 1966, Clark and Haviland 1977, Hornby 1974).
  • Embeddedness (Coleman 1966).

The cognitive theorists and linguists, beginning in the 1970s, promoted the idea that reading was largely an act of thinking. Among the ideas they promoted were:

  1. Meaning is not in the words on the page. The reader constructs meaning by making inferences and interpretations.
  2. Information is stored in long-term memory in organized "knowledge structures." The essence of learning is linking new information to prior knowledge about the topic, the text structure or genre, and strategies for learning.
  3. A reader constructs meaning using metacognition, the ability to think about and control the learning process (i.e., to plan, monitor comprehension, and revise the use of strategies and comprehension); and attribution, beliefs about the relationship among performance, effort, and responsibility (Knuth and Jones 1991).

The cognitive theorists, aware of the limitations of the readability formulas, set about to supplement them with ways to measure the content, organization, and coherence of the text. Their studies reinforced the importance of these variables for comprehension. They did not, however, come up with any practical method for measuring or adjusting them for different levels of readers.

The following sections summarize a few of these efforts.

Walter Kintsch and coherence Beginning in 1977, Walter Kintsch and his associates studied the cognitive and structural issues of readability. Kintsch proposed to measure readability by measuring the number of propositions in a text. A proposition consists of a predicate and one or more arguments. An argument can be a concept or another argument. A concept is the abstract idea conveyed by a word or phrase.

In the early part of his work, Kintsch (Kintsch and Vipond 1979) was quite critical of the readability formulas. He said they are not based on modern linguistic theory and they overlook the interaction between the reader and the text.