With the rise of contractions and the fall of “thus,” Liberman said this is illustrative of a larger, secular trend. “This obviously interacts with genre, and in particular with formality,” he said, stating that “won’t” appears much more frequently in magazines than “will not,” while less of a gap exists in academic papers.
State of the Union addresses incorporated contractions even later than secular dialogue, which hints at the level of formality presidents wish to project. Liberman suggested that the spoken version of the addresses may be more relaxed and contraction-laden than the much more prescribed written documents let on. “Perhaps Truman, Eisenhower and Kennedy were using contractions in their performances that were not written as such in their texts,” he said. The increased use of contractions suggests a growing laxity in the written documents rather than in spoken words.
The rise of “tonight,” Fields clarified, was simply the result of the State of the Union addresses occurring in the evening time for the first time with Lyndon B. Johnson’s 1965 address.