Fletcher Moulton LJ explained in British United Shoe Machinery Company Ltd, v A Fussell & Sons Ltd (1908) 25 RPC 631 at 650 how claims came to be incorporated into a patent specification and their purpose:
“As it is the duty of the inventor to give the fullest practical information to the public he is bound to put in, if, for instance the invention is a process, quantities and times which are the best he knows.
But it would be very cruel to hold him to the invention when carried out only with those best quantities and times, because a person could then take his invention in substance if he did not take it in quite the best way, and the value of the grant would be practically nothing. Hence inventors, in their own protection, took to introducing into their specifications language intended to distinguish between that which was there for the practical information of the public, and that which was there for delimitation of the invention.
Correct delimitation was of the greatest possible importance to the inventor, because if his Patent covered something which was old the Patent was wholly bad. At the same time there was the danger of confining himself to a mere outline which gave delimitation, but did not tell the public the best way within those limits of performing his invention. The one duty required him to state his invention in its most general form, and the other duty required him to state it in its best and therefore in a very special form.
Out of that has arisen the practice, which originally was perfectly optional, of having a separate part of the specification primarily designed for delimitation. That is what we call the Claim.”