Themes and revealers: using the puzzle's big idea

Most American crosswords published from Monday to Thursday, and almost every Sunday puzzle, are built around one idea. That idea is the theme, and it is the only part of the grid where the setter speaks to you directly. Find it early and the theme starts writing answers for you.

What a theme actually is

A theme is a rule that a small group of the longest answers all obey. Three to five entries follow it. The rest of the grid, which solvers and constructors both call the fill, has nothing to do with the theme and is there to hold the long entries in place.

Here is an example invented for this lesson. The long entries are CARBON COPY, SILVER LINING and IRON CURTAIN: ordinary phrases, each beginning with a chemical element. A fourth long entry, ELEMENTS OF STYLE, names the rule. The individual clues are unremarkable. The theme lives above them, in the pattern.

Where the theme entries sit

Grids have rotational symmetry, so theme entries come in symmetrical pairs. If an eleven letter entry runs across row 3, expect another across row 13. Before reading a single clue, note every slot of ten letters or more. In a 15 by 15 puzzle those slots are almost always the theme.

Theme entries usually run across, evenly spaced: rows 3, 8 and 13 in a light theme, rows 3, 6, 9 and 12 in a denser one. Sunday puzzles are 21 by 21 and may carry six to eight theme entries plus a title. The New York Times submission specifications set out the word counts and symmetry rules behind these shapes.

The revealer and how to read it

The revealer is the entry that names the trick. It is normally the last long across entry, low in the grid, and its clue gives itself away with a standard formula: a definition, then the words and a hint to, then a list of clue numbers. A revealer clue in the invented puzzle above might read: Strunk and White classic, or a hint to the starts of 17-, 26- and 44-Across.

Two habits follow. When you see clue numbers quoted inside another clue, jump to that clue at once. And if the revealer falls before the theme entries do, reread the theme clues with the rule in mind. They look different.

Theme families you meet early

Most themes belong to one of a few families, and learning the families is faster than learning puzzles.

• Sound change. A familiar phrase gains a letter or swaps a vowel, and the new phrase is clued at face value. These are usually flagged with a question mark, a convention covered in the lesson on clue punctuation and signals.
• Hidden words. Each theme entry buries a member of a category across its word breaks, for example a colour spanning the end of one word and the start of the next.
• Category. Every theme entry starts, ends or contains a member of a set: dog breeds, card games, units of time.
• Quote. A sentence split across three or four long entries. Hard to start, easy to finish, since half the sentence dictates the rest.

Rebus squares and Thursday tricks

A rebus is a square that holds more than one letter. American puzzles use them most often on Thursdays, the day reserved for gimmicks. You notice one by arithmetic rather than cleverness: you are sure of an answer and it is one or two letters too long for its slot. Check whether the crossing entry also wants an extra letter in the same square. When both do, write the whole group in that square, small on paper or through the rebus button in an app.

Other Thursday devices include entries that bend around a corner, entries that read backwards, and squares holding one letter across and a different one down. The Wordplay column explains each day's trick after publication, and the theme archive at XWord Info groups past puzzles by theme type.

Using the theme to finish the grid

Once you have the rule, the theme becomes a checksum. Write the remaining theme entries before returning to the short fill, since they carry the most crossing letters, then test each against the rule. An entry that fits its crossings but breaks the rule is wrong, and wrong in a way ordinary checking will not catch. That test clears more stalled corners than rereading does, which is why it appears in the working order for any grid.

Themed daily puzzles are the best practice ground, because their themes are consistent and legible. Solving a run of them, or reading the solutions afterwards at Daily Themed Crossword answers, builds the pattern recognition quickly. Fill, revealer and rebus are defined in the glossary.