Chaucer on Plain English

Speketh not in the heigh style, but so playn at this time,
I yow preye, that we may understonde what ye saye.

The Host to the Clerke of Oxenforde. Chaucer. Canterbury Tales. c. 1400.

Verbing

"First they came for the verbs and I said nothing, for verbing weirds language. Then they arrival for the nouns and I speech nothing, for I no verbs."

Attributed to Peter Ellis (via Diane Duane)

Eachard on Plain Language

As if plain words, useful and intelligible instructions, were not as good for an esquire, or one that is in commission from the King, as for him that holds the plough.

John Eachard, 1670. Some Observations Upon
the Answer to an Enquiry into
the Grounds and Occasions
of the Contempt of the Clergy.