It is well known that the way of counting the days of nida (woman that sees blood) for the Rambam is different than all other rishonim. The basic place that I recall shows the way of the Rishonim to be correct is Arakim 20.
The Mishna says אין פתח בטועה פחות משבעה ולא יותר מי''ז. [A woman that forgets the days of her period is not less than 7 and not more than 17]. And the Gemara goes on to explain it. The basic idea is lets says she see blood for a day. So you say that is the beginning of nida and you wait 17 more days. but even if she sees three days in a row that could be all zava or the last one could be the beginning of nida. In any case you never have more than 17. But the number goes down after 3. So each day after that she needs to count one day less. But To the Rambam this can not work. To his way the last day can always be the beginning of nida and she would need a whole 17 days.
[1-17;2-17;3-17;4-16;5-15;6-14;7-13;8-12;9-11;10-10;11-9;12-8;13-7]
The only thing I can imagine here is perhaps the Rambam simply found a different Gemara someone that to him implies that his way is correct.
The basic way of the Rishonim is that a woman that is once a zava never goes back to count nid until she has counted seven clean days This seems crytal clear in that Gemara in Arakim.
To see that the Rambam can not fit with the Gemara in Arakim take for example a woman that sees 13 days. With the Rambam the last day might be the beginning of nida. But that Gemara says she only needs then 7 clean days and then starts to count nida again. So the Rambam must have found someother place which he thought shows his way is correct.]
[The way of the Rishonim is seven days is nida [even if she sees only one day] and then mikve at the night of the start of the eight day. But if after that she sees for three straight days she is a zava and needs seven clean days. And she does not go back to nida until she has counted 7 clean days.
To the Rambam the cycle is always 7-11-7-11-7... unless she gives birth.
The Mishna says אין פתח בטועה פחות משבעה ולא יותר מי''ז. [A woman that forgets the days of her period is not less than 7 and not more than 17]. And the Gemara goes on to explain it. The basic idea is lets says she see blood for a day. So you say that is the beginning of nida and you wait 17 more days. but even if she sees three days in a row that could be all zava or the last one could be the beginning of nida. In any case you never have more than 17. But the number goes down after 3. So each day after that she needs to count one day less. But To the Rambam this can not work. To his way the last day can always be the beginning of nida and she would need a whole 17 days.
[1-17;2-17;3-17;4-16;5-15;6-14;7-13;8-12;9-11;10-10;11-9;12-8;13-7]
The only thing I can imagine here is perhaps the Rambam simply found a different Gemara someone that to him implies that his way is correct.
The basic way of the Rishonim is that a woman that is once a zava never goes back to count nid until she has counted seven clean days This seems crytal clear in that Gemara in Arakim.
To see that the Rambam can not fit with the Gemara in Arakim take for example a woman that sees 13 days. With the Rambam the last day might be the beginning of nida. But that Gemara says she only needs then 7 clean days and then starts to count nida again. So the Rambam must have found someother place which he thought shows his way is correct.]
[The way of the Rishonim is seven days is nida [even if she sees only one day] and then mikve at the night of the start of the eight day. But if after that she sees for three straight days she is a zava and needs seven clean days. And she does not go back to nida until she has counted 7 clean days.
To the Rambam the cycle is always 7-11-7-11-7... unless she gives birth.
