We've been discussing a large lumber distributor who commits to buy lumber from you at a price of $2.50, if he buys any lumber from you at all. Why is the distributor's commitment to pay you $2.50, even though the price could be lower in the future, not enough to support a legally enforceable bargain?

Write a few sentences explaining why this agreement is not a bargain. Try to include at least 1 of the 4 principles that might be relevant?