How many tactical patterns are there in chess?

Ahh . . . there's your answer.  2000 basic tactics patterns.  There's probably only about two dozen or so tactics categories -- but, @llama47 hit the nail on the head when he wrote:

Anyway, I imagine Heisman (or whoever he was referencing) was talking about standard manifestations of patterns. For example the Nc7 fork, or a Qa5 fork. These are patterns worth remembering because they happen over and over.

Bingo!  They would both be classified as a "fork".  But they are different patterns, and, as @llama47 said: they happen over and over again.

Another example of a tactical "pattern"

(If I've copied it correctly...) this is a well known smother-mate puzzle.   White to move.

But as a tactic it falls into a number of categories: "discovered check", "double check", "smother mate", etc.  The "pattern" is this particular configuration, and a combination of all three tactics.

(For those who haven't seen it before, try to solve it!)

I think that must be a famous example because although I don't remember where I saw it before I do recognize it from somewhere

1.Nh6++

1...Kf8 2.Qf7#

1...Kh8 2.Qg8 2...Rxg8 3.Nf7#

I have amended the forum topic. Yes this is what I meant: how many basic tactical patterns are there altogether and how many advanced tactical patterns are there?

I learned this week there are dozens of windmill patterns, all fun when you can spot them. Not all of them are with the rook and bishop. You can create a windmill with a knight and queen for example.

Infinite

Doesn't that famous Fischer-Byrne game feature a knight/queen windmill?

(Yeah, I know, there are two very famous Fischer-Byrne games -- I can't remember which one had it)

Donald.

The game against Robert is good, too.

That's a coincidence because I just posted about that Fischer-Byrne "Game of the Century" game yesterday: https://www.chess.com/forum/view/game-analysis/worlds-greatest-chess-games?page=1

From Dan Heisman's website -- note that he states that he erroneously heard that Dvoretsky said there were 2000 patterns, but Dvoretsky said that number didn't come from him, and now DH is not sure where he heard it from.  Nevertheless, I thought this to be a worthwhile web-page excerpt to post here:

From https://www.danheisman.com/recommended-book-lists.html

"Dvoretsky" Set
A set of tactics books which together may contain 97% of the ~2,000 basic tactics patterns (*= good three to start):

• Chess Tactics for Students                             - John Bain* (can do repetitively - for details on how to do this book, see my Book Recommendation page)
• Bobby Fischer Teaches Chess                        - Bobby Fischer and Margulies*
• Starting out: Chess Tactics and Checkmates - Chris Ward*
• Winning Chess Strategy for Kids                   - Jeff Coakley (a great author)
• The Chess Tactics Workbook                         - Al Woolum
• Back to Basic: Tactics                                     - Dan Heisman (use cleaned-up 3rd printing 2018)
• The Winning Way                                            - Bruce Pandolfini (more difficult to find)
• Power Chess for Kids                                      - Hertan - a helpful book about how to find basic forcing moves, easier than Hertan's also very good Forcing Chess        Moves; check out Hertan's helpful essay "Adventure and Sportsmanship" on p.13, but his key exception on p.19 has exceptions itself!

Need more basic patterns? Throw in:

• Checkmate for Children by Kevin Stark has an excellent array of basic checkmate patterns
• The Art of the Checkmate by Renaud and Kahn
• Winning Chess Traps - Irving Chernev
• Winning Chess Tactics - Seirawan & Silman - not a great problem set, but good explanations of the Tactics - in that sense similar to Learn Chess Tactics by Nunn

 A book with book stragegy and tactics (and no hint of what the problem requires is Practical Chess Exercises by Cheng - An interesting idea with 600 positions from games where all you are given is that there is a best move. It could be the only saving defensive tactic, play and win, or a positional idea.
Novice Nook on why using these puzzles to reject your candidate moves is the main idea for studying basic tactics
 IM David Pruess's interesting insights on the 2,000 basic patterns
 Dvoretsky denies the idea of 2,000 basic patterns came from him (link no longer working and removed)

I've often wondered about that same comment--"2,000 ... tactics patterns."

I think we need to ask Mr. Heisman. Maybe he means 2,000 root positions with many more minor variations. There might be two or three different patterns related to the center-fork trick. And there might be a few more involving Bxf7+ in the opening. Perhaps the Greek Gift would be only one single pattern, but, for some, it is at least six (arguably 20 or more) different patterns.

The Checkmate Patterns Manual identifies more than 30 (but some of those include more than one pattern).

I noticed how Neishtadt ("Improve Your Chess Tactics") selects groups of positions by the preparatory move(s): deflection; decoy; decoy AND deflection; square clearance; diagonal clearance; diagonal clearance AND eliminate defender; interference; etc...

Of course, we start with the big ones: pin, x-ray (or skewer), fork (or double attack), discovered attack, attacking the defender (or undermining), and trap.

I only recently learned that "square closing" is a term (used when we decoy an enemy piece to a square where the opponent's king would otherwise flee from mate).

So what does that leave us with? another 1,912 patterns?

Let's see. After the opponent castle's short, there's Qg4 followed by Bh6 (or Bxh6); there's the Bc2 & Qd3 battery on h7... Prior to castling there are the forks & traps involving the undefended rook on its starting square...

Hans Kmoch's Pawn Power in Chess drew my attention to the concept of "sealing"; which is a tactical motif that involves luring an opposing Pawn to a specific square in order to deny the opponent's pieces the use of that same square. It is based on the idea that you cannot capture your own Pawns.

Example:

I've read My System. I would recommend it to anyone. As well as Pawn Power by Smoch and 5334 chess problems by Polgar. I am half way through that one. Big book but I like the fact that it is actual mates from real games.

Most of Polgar are compositions. The 600 games at the back of the book are real games.

as many as patterns or groups of patterns defining an unique idea