"among your sons shall you redeem": What is the intent of this? It is written (Numbers 18:16) "And redemption from one month"—general. "according to the monetary valuation, five shekalim"—particular. (In sum,) general-particular: (the rule is:) The general contains only what is (specifically) in the particular. And (Exodus 13:13) "Every human first-born among your sons shall you redeem" reverts to the general. But perhaps (instead of reversion to the general) it is added to the first generalization (i.e., "And his redemption from one month, etc.", where the rule is as indicated above)? Would you say that? Rather, (it is perceived as) general-particular-general, where the rule is: The general is of the nature of the particular, viz.: Just as the particular is movable, not mortgaged, and of monetary value in itself, so I will include all such property (as valid for redemption of one's son.) From here they ruled: All is valid for the redemption of a man's first-born, except for bondsmen, bills, land, and consecrated property.