“The strengthening of behavior which results from reinforcement is appropriately called "conditioning."”
In operant conditioning we "strengthen" an operant in the sense of making a response more probable or, in actual fact, more frequent.
Science and Human Behavior (1953)
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B.F. Skinner 30
American behaviorist 1904–1990Related quotes

“Is it ‘Moran’ or ‘Moron’?” http://www.ilanamercer.com/phprunner/public_article_list_view.php?editid1=552 WorldNetDaily.com, May 28, 2010].
2010s, 2010

Source: The German Ideology (1845-1846), Vol. I, Part 1.
Source: The Culture of Make Believe (2003), p. 50

“…conditioning usually reinforces instinct rather than overrides it.”
Source: The Red Queen (1993), Ch. 6

2010s, 2011, Speech at the Gerald R. Ford Foundation (2011)

“Here is bread, which strengthens man's heart, and therefore called the staff of life.”
Psalm 104.
Commentaries

Source: 1940s, Quasi-Stationary Social Equilibria and the Problem of Permanent Change, 1947, p. 40.