A particular lien is a right to retain goods until all charges in respect of those goods have been paid. Common carriers have a lien in respect of the freight on goods carried. A particular lien does not arise unless: the work has been completed, except when the owner prevents completion, and the chattel (i.e. the thing) has been improved by the work or the expenditure. An agreement to maintain a motor car does not amount to improving it so that the person responsible for maintenance has no lien – Hatton v Car Maintenance Co. Chattels are all personal property (not realty) which is tangible, i.e. actual things which one owns or possesses. Things which a person owns or possesses which are not tangible, for example a debt, an interest in shares, are known as ‘chose in action’. At common law, the shipowner is entitled to a possessory lien on cargo for freight payable on delivery. The shipowner is similarly entitled to a lien for general average contributions and for extraordinary expenses which have been justifiably incurred for the protection of cargo. These common law liens are all possessory in nature: in other words, the shipowner’s right is to retain possession of the goods until, for example, the freight due is offered to him. Since the common law lien for freight is only possessory, it can be waived or lost by, for example, delivering the goods to the person entitled without insisting on payment. There is no common law or implied lien in respect of freight which is contractually payable either before (advance freight) or after delivery. Neither is there any lien at common law for deadfreight nor for demurrage or damages for detention. But liens for advance freight, demurrage, deadfreight and other items, (‘all other charges’) can be and frequently are created by agreement. This sort of lien created by agreement would be a contractual lien.