In its strict sense a fable is a short story or folk tale embodying a moral, which may be expressed explicitly at the end as a maxim.
"Fable" comes from Latin fabula (meaning 'conversation', 'narrative', 'tale') and shares a root with faber, "maker, artificer." Thus, though a fable may be conversational in tone, the understanding from the outset is that it is an invention, a fiction.
A fable may be set in verse, though it is usually prose.
The constancy of the laws of nature, or the certainty, with which we may expect the same effect, from the same causes, is the foundation of the faculty of reason.
The constancy of the laws of nature, is the foundation of the industry and foresight of the husbandman; the indefatigable ingenuity of the artificer; the skilful researches of the physician, and anatomist; and the watchful observation, and patient investigation, of the natural philosopher.
To this constancy we owe all the greatest, and noblest efforts of intellect.