The next (and final) group of melachos has to do with the assembling, disassembling and transporting of the Mishkan. Remember, the Mishkan was a portable Temple that was taken down as needed and moved from place to place, where it was then re-assembled. The Mishkan was made up of 48 boards that fit together with pegs and sockets. These boards had to be assembled in their proper order so they were marked to identify them. (For example, one board might be marked AB, the next BC, the next CD, etc. so that one would know that the A’s are adjacent, as are the B’s, the C’s, etc.) Putting these identifying marks on the boards entailed writing, the melacha of koseiv.
Koseiv involves creating any meaningful letter or symbol. It doesn’t have to be with ink on paper. A rubber stamp, carving into stone or cutting a letter out of paper all involve koseiv. Even forming a letter out of something temporary – such as those toys where one uses a magnet to manipulate iron filings – is prohibited on Shabbos under this melacha. Koseiv applies to letters or symbols in any language, including Braille, Morse code and the like.
The Biblical prohibition only applies to permanent writing. Temporary writing is prohibited rabbinically. So breathing on a window to fog it up then writing on it with one’s finger (for example) is prohibited at the rabbinic level.
Since koseiv involves making meaningful symbols, not just letters, assembling a puzzle on Shabbos is problematic for an adult. Photography is likewise prohibited on Shabbos for this reason. Forming words out of existing letters is also an issue. Accordingly, those who play such games as Scrabble on Shabbos should be careful to maintain a small space between the letters. Games that hold the letters locked in place (such as Deluxe Scrabble and Boggle) are not permitted because of koseiv.
We do not conduct business on Shabbos in large part because of koseiv, as one typically writes such things down. Incidental writing, such as leaving the name of a shoe company imprinted in the mud by the soles of one’s shoes, is not a problem; one doesn’t particularly desire or benefit from this outcome, so the rabbinic restriction on temporary writing was not imposed in such a case.
This is just an introduction to the concepts of the melacha of koseiv; it is not a substitute for a full study of the halachos.