Must a debt under a contract be ascertainable in order to be called a debt?

Defining 'debt' for the purpose of contract interpretation

If a 'debt' needs to be defined or ascertained for the purpose interpreting a provision of the contract, then the definition of 'debt' will be governed by the normal Rules of contract interpretation and construction. There are five principles of interpretation used by the courts when it is seeking to discover what a contract means, these were formulated by Lord Hoffmann in the leading case of Investors Compensation Scheme v West Bromwich Building society ('ICS') .

These five principles were later summarised by Lord Bingham in BCCI v Ali:

‘To ascertain the intention of the parties the court reads the terms of the contract as a whole, giving the words used their natural and ordinary meaning in the context of the agreement, the parties’ relationship and all the relevant facts surrounding the transaction so far as known to the parties. To ascertain