Owner claimed he did not understand he was dealing with a corporation. Although contract and invoice set out trade name only, contrary to section 2(6) of the Ontario Business Names Act, the corporate contractor had registered the trade name. Contractor testified he had told owner about corporation. Normally, an attack on corporation is to establish personal liability for the principal. In this case, the owner was defending against the contractor’s valid claim for money due to it. The judge held that there was no hardship to the owner from fact that corporate name was not shown on invoice and held the owner liable.