E. E. Harriman: I usually think of an incident, a situation, and roll it over like a snowball until it accumulates enough to make it a story.
Nevil G. Henshaw: I've no fixed rule, although, in a long piece of work, I try to present a certain section with its corresponding inhabitants and industries. With short stories I either work from a single plot idea, or propound a certain phase of human character and set out to prove it by means of the story—(as in Madame Justice I endeavored to give certain conditions under which a mother would kill her well-beloved son).
Joseph Hergesheimer: It grows from the emotion caused by a place or an individual.
Robert Hichens: Usually some big situation arising from the clash of two characters.
R. de S. Horn: The genesis of a story with me is generally an incident, a situation, or a character or trait of character, with the incident predominant. I have some settings tucked away in my note-book, but I expect they will be used only when I've got a situation, character or incident idea to go with them. The title is the last thing I write usually, and it generally comes hardest. However sometimes I stumble on it in the middle of the story. Every idea that suggests a story possibility I immediately enter in my note-book.
Clyde B. Hough: My story ideas generally grow out of a phrase or a sentence and this phrase or sentence most often takes its place in the story, either as the core, the hinging base or the climax. This sort of plot germ is generated in various ways. Sometimes by a scene, sometimes by a spoken word and sometimes by a man's action.
Emerson Hough: Some big motive or period. Not a Peeping Tom incident.
A. S. M. Hutchinson: Character entirely.
Inez Haynes Irwin: It is very difficult for me to tell you what I mean by the idea for a story. There is so much to say that I would like to answer this question in a book. That idea may come from anywhere or grow from anything. It may be as you suggest "an incident, a character, a trait of character, a situation, a setting, a title." It may come through a conversation, by analogy, out of the very air itself. In my experience a single scene has suddenly amplified to a whole story, a whole novel has suddenly diminished to a story. Parts of stories, quite disconnected, have suddenly sprung together and made one complete story. I have had the experience of having two or three stories develop in successive instants from a single germ; sometimes I have waited years before writing because I could not decide which one of them was the best. Mere ideas that I have carried in my mind for years have suddenly developed into stories. Mere phrases and titles have spawned stories. Interiors, empty houses, geographical situations have exploded stories. Stories, full grown, have sprung without any warning into my consciousness; and apparently with no spiritual or psychological raison d'etre. I have even had stories, all complete, hurtle out at me from life itself. Reading the stories of other authors sometimes brings stories into my mind; their first paragraphs are occasionally exceedingly stimulating. Certain ideas have always been highly stimulating to me—uninhabited islands, ghosts, fourth dimension, murder, they have engendered numberless stories. In brief stories come in every way and through every medium. Everything on earth, under the earth and above the earth is fish to the creative artist's net.
I would like to illustrate every one of the above statements but it would make the answer to your first question interminable.