E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Simplicity is sine plica,
without a fold; as duplicity is duplex plica, a double fold. Conduct without a fold is straightforward, but thought without a fold is mere childishness. It is tortuity of thought that constitutes philosophic wisdom, and simplicity of thought that prepares the mind for faith.
The flat simplicity of that reply was admirable.Vanbrugh and Cibber: The Provoked Husband, i.