Under the common law the shipper owes an absolute duty not to deliver for the shipment the goods of a dangerous nature without expressly giving notice that they are of a dangerous nature. It was, however, disputed for many years whether absence of knowledge or means of knowledge on the part of the shippers is a good defence against the owners’ claim.
Definition of inherent vice or nature of the subject matter insured was given by Lord Diplock in Soya GmbH Mainz Kommanditgesellschaft v White  1 Lloyd’s Rep 122 at p.126:
The facts as I have summarized them for the purpose of determining the question of construction of the HSSC policy in the instant case, assume that the loss resulting from the deterioration of the soya beans during the voyage was proximately caused by the "inherent vice or nature of the subject-matter insured". This phrase (generally shortened to "inherent vice") where it is used in s. 55 (2) (c) refers to a peril by which a loss is proximately caused; it is not descriptive of the loss itself. It means the risk of deterioration of the goods shipped as a result of their natural behaviour in the ordinary course of the contemplated voyage without the intervention of any fortuitous external accident or casualty. Prima facie, this risk is excluded from a policy of marine insurance unless the policy otherwise provides, either expressly or by necessary implication, and the question of construction for your Lordships is whether the standard HSSC policy does otherwise provide.
Per Lord Mance in Global Process Systems Inc & Anor v Berhad  UKSC 5 at para 80:
If inability to withstand foreseeably bad weather conditions does not prevent damage sustained as a result being attributed to perils of the sea,
(i) that must be because Lord Diplock’s reference to "the ordinary course of the contemplated voyage" was not intended to embrace the weather conditions foreseeable on such a voyage, but was rather used as a counterpoint to a voyage on which some fortuitous external accident or casualty occurred and
(ii) there is no apparent limitation in Lord Diplock’s qualification "without the intervention of any fortuitous external accident or casualty" – in other words, on the face of it, anything that would otherwise count as a fortuitous external accident or casualty will suffice to prevent the loss being attributed to inherent vice.