Shabbos 112a - Making Knots

The Mishna teaches that there are 3 types of knots, some are assur m'doraysa, some m'drabonon, and some are permitted. Rashi and the Rosh explain that any knot which is permanent and meant to be there for an unlimited amount of time is considered a permanent know for which one is chayev m'doraysa. Knots that are semi-permanent and meant to stay for a short but significant amount of time are assur m'drabonon, and knots that are non-permanent are permited. The Rama bring two opinions as to the exact criteria for differentiating the second and third category. Some hold that if it is meant to be untied daily it is mutar, but otherwise it is in category 2 and assur m'drabonon, and some hold that if it is meant to last for less than 7 days it is mutar, but longer than 7 days is category 2 and assur m'drabonon. These two opinions develop from contradictory diyukim from Rashi in our sugya. 

The Taz cited by the Biur halacha 317:1 assumes that the permanence is dependent on the persons intent when he ties the knot. So long as the intent is to be temporary, even if it is the type of knot tied normally for permanence, and even if itis tied by an expert, it is not a Torah violation. But the Biur Halacha disagrees and cites from the Beis Meir that the type of knot which is normally tied as a permanent knot, one is chayev for even if the person tying it doesn't intend to keep it permanently. It seems from the Biur Halacha that intent has the ability to consider a knot which is generally tied as a temporary knot, to be a permanent knot and be chayev, but will not remove the Torah prohibition from tying a knot that is normally tied to be permanent. With this he explains why it is impossible to tie tzitzis on shabbos without violating shabbos, since even if the person tying intends to take out the knots after shabbos, it will still be a Torah violation.

The Rif and Rambam have an entirely different approach. They hold that there are 2 criteria for knots, permanence and an expert knot. When both criteria are met, meaning the knot is permanent and the type made by an אומן, it is an issur d'oraysa. If it is either a permanent know OR a ma'aseh uman it's assur m'drabonon, and only if it is neither is it permitted. However, within this approach there is no room to distinguish between various levels of permanence. Therefore, even if one intents the knot to be there for a few weeks or months, but not permanently, so long as it is not a מעשה אומן, it is permitted (M.B. 317:5). Based on the opinion of the Rambam and our lack of knowledge what is considered to be a מעשה אומן, the Rama says that it is forbidden to tie any double knot since there is concern that it qualifies as a מעשה אומן which is assur m'drabonon even if not done as a permanent knot.

All opinions agree that there is not distinction how tight the knot is. Only R. Meir in the Mishna has a clause that if it is so loose that one can untie it with one hand, it isn't considered a knot, but the Rabbonon don't consider that to be an important factor (so long as it is tight enough that it won't untie by itself).