w the reason why that day in particular
is fixed upon, rather than the day before or after. But a custom that
no cattle shall be put in till the lord of the manor has first put in
his, is unreasonable, and therefore bad: for peradventure the lord
will never put in his; and then the tenants will lose all their
profits[n].

[Footnote l: Litt. Sec. 212.]

[Footnote m: 1 Inst. 62.]

[Footnote n: Co. Copyh. Sec. 33.]

5. CUSTOMS ought to be _certain_. A custom, that lands shall descend
to the most worthy of the owner's blood, is void; for how shall this
worth be determined? But a custom to descend to the next male of the
blood, exclusive of females, is certain, and therefore good[o]. A
custom, to pay two pence an acre in lieu of tythes, is good; but to
pay sometimes two pence and sometimes three pence, as the occupier of
the land pleases, is bad for it's uncertainty. Yet a custom, to pay a
year's improved value for a fine on a copyhold estate, is good: though
the value is a thing uncertain. For the value may at any time be
ascertained; and the maxim of law is, _id certum est, quod certum
reddi potest_.

[Footnote o: 1 Roll. Abr. 565.]

6. CUSTOMS, though established by consent, must be (when established)
_compulsory_; and not left to the option of every man, whether he will
use them or no. Therefore a custom, that all the inhabitants shall be
rated toward the maintenance of a bridge, will be good; but a custom,
that every man is to contribute thereto at his own pleasure, is idle
and absurd, and, indeed, no custom at all.

7. LASTLY, customs must be _consistent_ with each other: one custom
cannot be set up in opposition to another. For if both are really
customs, then both are of equal antiquity, and both established by
mutual consent: which to say of contradictory customs is absurd.
Therefore, if one man prescribes that by custom he has a right to have
windows looking into another's garden; the other cannot claim a right
by custom to stop up or obstruct those windows: for these two
contradictory customs cannot both be good, nor both stand together. He
ought rather to deny the existence of the former custom[p].

[Footnote p: 9 Rep. 58.]

NEXT, as to the allowance of special customs. Customs, in derogation
of the common law, must be construed strictly. Thus, by the custom of
gavelkind, an infant of fifteen years may by one species of
conveyance (called a deed of feoffment) convey away his lands in fee
simple, or f