Nazir 41: Positive Mitzvot Override Negative Mitzvot; On Razors and Mixed Fibres

We learn about how to balance contrasting positive and negative mitzvot.  Nazirites are commanded to grow their hair and to shave their heads following their nazirut - these are positive mitzvot.  Lepers are commanded to shave all of their hair at the conclusion of their time away from community - another positive mitzvah.  Men are commanded to avoid cutting the corners of their hair and the corners of their beards - these are negative mitzvot. 

What should nazirites or lepers do when they are commanded both to cut their hair and to leave their hair to grow without being cut?

The rabbis explain the principle of "aseh docheh lo ta'aseh", a positive mitzvah overrides a negative mitzvah.  Of course if it is possible to accommodate both mitzvot, one should attempt to do so.  But when a nazirite is meant to shave his head, that positive mitzvah overrides the prohibition against cutting the corners of the hair on his head.

The rabbis look at these prohibitions against cutting the corners of one's head or beard in greater detail.  They also examine the differences implied between cutting hair with a razor or with other tools, such as a plane or a tweezer.  The fact that the razor is mentioned specifically in a number of circumstances helps the rabbis determine that the razor itself is important; the prohibition against cutting the corners of one's hair and beard does not extend to other instruments.

Our daf ends with the origin of the principle of aseh docheh lo ta'aseh.  The tallit, prayer shawl, is commanded to be made of one fibre; wool and linen should not be combined in its construction.   At the same time, the tzitzit, fringes of the tallit are commanded to be made from wool and blue dye.  Thus the negative commandment regarding combining two fibres can be overridden by the positive commandment to fashion tzitzit from wool, which very well may combine with a linen tallit.