The points to be made here are two, and they are both important. The first is that the writer must deal in sense detail. The second is that these must be details "that matter." As a writer of fiction you are at constant pains not simply to say what you mean, but to mean more than you say. Much of what you mean will be an abstraction or a judgment. But if you write in abstractions or judgments, you are writing an essay, whereas if you let us use our senses and do our own generalizing and interpreting, we will be involved as participants in a real way. Much of the pleasure of reading comes from the egotistical sense that we are clever enough to understand. When the author explains to us or interprets for us, we suspect that he or she doesn't think us bright enough to do it for ourselves.

A detail is concrete if it appeals to one of the five senses; it is significant if it also conveys an idea or a judgment or both. The window sill was green is concrete, because we can see it. The window sill was shedding flakes of fungus-green paint is concrete, and also conveys the idea that the paint is old and suggests the judgment that the color is ugly. The second version can also be seen more vividly.

Here is a passage from a young writer, which fails through lack of appeal to the senses.

Debbie was a very stubborn and completely independent person, and was always doing things her way despite her parents' efforts to get her to conform. Her father was an executive in a dress manufacturing company, and was able to afford his family all the luxuries and comforts of life. But Debbie was completely indifferent to her family's affluence.

This passage contains a number of judgments we might or might not share with the author, and she has not convinced us that we do. What constitutes stubbornness? Independence? Indifference? Affluence? Further, since the judgments are supported by generalizations, we have no sense of the individuality of the characters, which alone would bring them to life on the page. What things was she always doing? What efforts did her parents make to get her to conform? What level of executive? What dress manufacturing company? What luxuries and comforts?

Debbie would wear a tank top to a tea party if she pleased, with fluorescent earrings and ankle-strap sandals.
  "Oh, sweetheart," Mrs. Chiddister would stand in the doorway wringing her hands. "It's not nice."
  "Not who?" Debbie would say, and add a fringed belt.
  Mr. Chiddister was Artistic Director of the Boston branch of Cardin, and had a high respect for what he called "elegant textures," which ranged from handwoven tweed to gold filigree, and which he willingly offered his daughter. Debbie preferred her laminated wrist bangles.

We have not passed a final judgment on the merits of these characters, but we know a good deal more about them, and we have drawn certain interim conclusions that are our own and not forced on us by the author. Debbie is independent of her parents' values, rather careless of their feelings, energetic, and possibly a tart. Mrs. Chiddister is quite ineffectual. Mr. Chiddister is a snob, though perhaps Debbie's taste is so bad we'll end up on his side.

But maybe that isn't at all what the author had in mind. The point is that we weren't allowed to know what the author did have in mind. Perhaps it was more like this version.

One day Debbie brought home a copy of Ulysses. Mrs. Strum called it "filth" and threw it across the sunporch. Debbie knelt on the parquet and retrieved her bookmark, which she replaced. "No, it's not," she said.
  "You're not so old I can't take a strap to you!" Mr. Strum reminded her.
  Mr. Strum was controlling stockholder of Readywear Conglomerates, and was proud of treating his family, not only on his salary, but also on his expense account. The summer before he had justified their company on a trip to Belgium, where they toured the American Cemetery and the torture chambers of Ghent Castle. Entirely ungrateful, Debbie had spent the rest of the trip curled up in the hotel with a shabby copy of some poet.

Now we have a much clearer understanding of stubbornness, independence, indifference, and affluence, both their natures and the value we are to place on them. This time our judgment is heavily weighed in Debbie's favor-partly because people who read books have a sentimental sympathy with people who read books-but also because we hear hysteria in "filth" and "take a strap to you," whereas Debbie's resistance is quiet and strong. Mr. Strum's attitude toward his expense account suggests that he's corrupt, and his choice of "luxuries" is morbid. The passage does contain two overt judgments, the first being that Debbie was "entirely ungrateful." Notice that by the time we get to this, we're aware that the judgment is Mr. Strum's and that Debbie has little enough to be grateful for. We understand not only what the author says but also that she means the opposite of what she says, and we feel doubly clever to get it; that is the pleasure of irony. Likewise, the judgment that the poet's book is "shabby" shows Mr. Strum's crass materialism toward what we know to be the finer things. At the very end of the passage, we are denied a detail that we might very well be given: What poet did Debbie curl up with? Again, by this time we understand that we are being given Mr. Strum's view of the situation and that it's Mr. Strum (not Debbie, not the author, and certainly not us) who wouldn't notice the difference between John Keats and Stanley Kunitz.