Variables and Quantifiers:
Now we have to diagnose now that if we wanted to say that there is a meal at the Red Lion which costs only 3 pounds, is well sayed. Rather thenif we said that cost_of(meal, red_lion) = three_pounds, that is on this states that a particular meal (a constant, which we've labeled meal) costs 3 pounds. That does not accurately capture what we wanted to say. Just to a start, it implies in which side we know exactly which meal it is that costs 3 pounds, and however, the landlord at the Red Lion chose to let this the bizarre name of "meal". Furthermore it doesn't convey the fact that there may be more than one meal which costs 3 pounds.
In fact instead of using constants in our translation of the sentence could like we should have used variables as "there is a meal at the Red Lion costing 3 pounds". Nevereather than if we had replaced meal with something that reflects the fact that we are talking about a generic, rather than a specific meal, so things would have been clearer. Wherever a predicate relates something that be vary i.e. like our meal, than we call these things variables, so represent them with an upper-case word or letter.