building he is erecting, entitled to recover from the adjoining owner
who used the wall. Nor can anything be recovered from the owner of a
vessel by the underwriters who had her docked for repairs though by
such docking the owner gained an important benefit. Nor can one who in
pumping out his quarry frees another quarry from water recover
anything for the service. Nor can one who is benefited by experiments
made by another to test the value of patented inventions, in which
both are interested, be legally required to pay for the benefit he has
received.

As no expectation of payment does presumptively arise when services
are rendered by one member of a family to another member, one who
claims payment for them must prove that they were not rendered as a
gratuity, but on the legal supposition that he had a right to
compensation.

One who knows or who has reason to believe that compensation is
expected for goods or services tendered to him ought not to accept
them unless he intends to pay for them. If he does his act of
acceptance will be regarded as a promise of payment, and can be
enforced. But if one accepts goods or services without knowledge or
reason to believe that compensation will be expected, what then?
Suppose A sends a barrel of apples to B supposing, from their previous
course of dealing, that B will return them if he does not want them? B
should either return them or pay. Suppose B is misinformed and learns
that A is giving a barrel of apples to each of his customers? Then he
would be justified in keeping them until he learned the truth.

If, in making a contract it is taken for granted by both parties that
a certain fact exists, which, if not existing, would make the contract
impossible of execution, the contract is void. Thus, in contracts for
the sale of specific personal property, its existence at the time of
the sale is generally assumed. If the property has perished or been
destroyed, the contract is void. The same rule has been applied to the
sale of non-existent reality, of the transfer of void or spurious
securities, of the assignment of a void lease. In all these cases the
money paid in misreliance on the void contract is recoverable.

Premiums paid on a policy of marine insurance by one who in reality
had no goods on board, or for a voyage that was never begun, may be
recovered. The existence of a risk is assumed by both parties, in fact
there is no risk, consequently there was nothing to which