Constants - first-order logic:
Constants are things that is cannot be changed, like as england, black and barbara. So then they stand for one thing only, so that can be confusing whenever the constant is something blue, for why is cause we know there are different shades of blue. In fact we are going to talk about other type of shades of blue in our sentences, moreover, we should not have made blue a constant, but after used shade_of_blue as a predicate, in that we can specify some constants, like as navy_blue, aqua_marine and so on. However to translating a sentence into first-order logic, one of the first things we must decide what kind objects are to be the constants. One conference is to use lower-case letters for the constants in a sentence, for that we stick too and more.