"Even when a document (or relevant part of a document) is intended by the parties to be legally binding, there are circumstances in which it may be regarded as too uncertain to be enforceable by a court. Such a conclusion should, however, be one of last resort. English law aims to uphold and give effect to the intentions of the parties, not to defeat them. As Lord Tomlin observed in Hillas & Co Ltd v. Arcos Ltd (1932) 43 Ll.L.Rep. 359, 364, the aim of the court 'must always be so to balance matters that, without violation of essential principle, the dealings of men may as far as possible be treated as effective, and that the law may not incur the reproach of being the destroyer of bargains.' Accordingly, where the court is satisfied that the parties intended that their bargain should be enforceable, it will strive to give effect to that intention by construing the words used in a way which gives them a practical meaning: see e.g. Brown v. Gould[1972] Ch. 53 , 56-58; BJ Aviation Ltd v Pool Aviation Ltd[2002] EWCA Civ 163 , [2002] 2 P. & C.R. 25, para 23; Maple Leaf Macro Volatility Master Fund v. Rouvroy[2009] EWHC 257 (Comm) , [2009] 1 Lloyd's Rep. 475, para 235; Barbudev v. Eurocom Cable Management Bulgaria EOOD and others[2012] EWCA Civ 548 , para 32."
"In my judgment the following principles relevant to the present case can be deduced from these authorities, but this is intended to be in no way an exhaustive list: Each case must be decided on its own facts and on the construction of its own agreement. Subject to that: 1. Where no contract exists, the use of an expression such as 'to be agreed' in relation to an essential term is likely to prevent any contract coming into existence, on the ground of uncertainty. This may be summed up by the principle that 'you cannot agree to agree'. 2. Similarly, where no contract exists, the absence of agreement on essential terms of the agreement may prevent any contract coming into existence, again on the ground of uncertainty. 3. However, particularly in commercial dealings between parties who are familiar with the trade in question, and particularly where the parties have acted in the belief that they had a binding contract, the Courts are willing to imply terms, where that is possible, to enable the contract to be carried out. 4. Where a contract has once come into existence, even the expression 'to be agreed' in relation to future executory obligations is not necessarily fatal to its continued existence. 5. Particularly in the case of contracts for future performance over a period, where the parties may desire or need to leave matters to be adjusted in the working out of their contract, the Courts will assist the parties to do so, so as to preserve rather than destroy bargains, on the basis that what can be made certain is itself certain. Certum est quod certum reddi potest. 6. This is particularly the case where one party has either already had the advantage of some performance which reflects the parties' agreement on a long term relationship, or has had to make an investment premised on that agreement. 7. For these purposes, an express stipulation for a reasonable or fair measure or price will be a sufficient criterion for the courts to act on. But even in the absence of express language, the Courts are prepared to imply an obligation in terms of what is reasonable."