Linear relationships can be captured with a straight line on a graph. Linear relationships are easy to think about.... Linear equations are solvable... Linear systems have an important modular virtue: you can take them apart, and put them together again — the pieces add up.

p. 23 as cited in: James R. Hansen (2004), Trees of Texas: An Easy Guide to Leaf Identification, p. 246 - Chaos: Making a New Science, 1987