Knives
Knives and daggers were used less for combat and more as tools by the 18th century. All manners of frontiersman, homesteader and laborer needed knives in their daily life. Scale tang knives were the most common knives in the 18th century. They were easy to make, had blades between six and nine inches and had simple wood, bone or antler handles. Scale tang knives had a hole drilled into the handle and the tang (the metal part of the blade that goes into the handle) locked in place with a pin in the middle of the handle. Round tang knives were similar except the handle was cut intentionally short so a locking mechanism could be affixed to the base.
Bayonets
Bayonets were the evolution of the infantry soldier's knife or sword. Bayonets had mounting mechanisms that allowed them to be affixed to the barrel of a rifle converting it into a large bladed spear after the opportunity to fire bullets had passed. Often used after multiple rounds of volley, the order to "fix bayonets" was given and the infantry was ordered to charge or brace to receive a charge. Appearing as swords and knives, bayonets could be used to fight without attaching them if the fight was dire and continued to see usage for hundreds of years.
Saber
First seen in the hands of the Hungarian Light Cavalry, known as Hussars, the saber became a necessity for the 18th century cavalryman. According to French cavalry commander General Chablis, "The saber is the cavalryman's science of survival." The saber has a sharpened blade as well as a thrusting point allowing it to both cut and stab; it also has a slightly curved blade. With the unwieldiness of the rifle from horseback, the more elegant saber was used by mounted troops for years.
Rapier and Small Sword
The rapier saw its final days in the early 1700s. Having come about as the premier dueling sword, or gentleman's sword, when firearms had rendered armor useless, the rapier was the choice blade for duelists for a long time. In the 18th century, however, the small sword was developed. The small sword was a thinner, lighter and therefore faster blade that made the formerly elegant rapier look bulky in comparison. Both of them lost popularity as pistol dueling emerged as the new way that gentlemen settled their slights of honor.