Lift the cushions of the settee if possible. Look for a manufacturer's stamp on the wood below the cushions or underneath the settee. The maker's stamp and date may also be on the back of the settee.
Inspect the craftsmanship of the settee. Look at any hardware such as nails and screws. If your settee has screws, it may not be an antique or it may have been restored at a later time, as screws were not used until the 20th century.
Feel the back of the settee's wood and upholstered areas. If the furniture has very sharp edges and corners, it is likely more recently manufactured. Antiques generally have softer and more rounded edges.
Check whether the carpentry of the settee was handcut and carved where pieces of wood have been joined together. Furniture pieces made by hand will show slight variations while machine cut pieces will more likely be the same. Dovetailing, a type of interlocking mechanism to join furniture together, was also often used to make antique furniture. This type of joint is often found in antique desks and drawers; it may also be found in your settee where the back and front wooden pieces are joined to the sides. A carpenter or antiques dealer can likely tell you if your settee has this type of construction.
Make an appointment with an antiques appraiser who can determine whether your settee is antique. Inform him of any history that you know about the piece, such as it belonged to your grandmother and where it came from. An appraiser is trained to look for certain signs that can determine the age and type of a piece of furniture.