Here is a very clear and easy way to identify furniture.
The "period" of furniture denotes the approximate dates between which a piece was manufactured. Periods are named for their designer or reigning monarch of the time. The word "style" groups furniture designed similarly to pieces made in a particular era. "Characteristics" are the particular points of similarity among furniture of a certain style. From period to period, there is some overlap. Periods went through a time of transition from one to another and furniture made during these overlaps is called "transitional". A transitional piece having characteristics of two periods can be interesting to date.
The William and Mary period (1700-1725) is best characterized by the turnip foot, ball foot or trumpet turning and the Spanish foot found on chairs. The woods used in this period were predominantly walnut, oak and maple. The hardware used on this furniture is best characterized by the teardrop pull.
The Queen Anne period (1725-1760) is best characterized by the snake foot and cabriole legs. The woods used during this period were predominately walnut, maple, and cherry. The hardware accompanying this period is best characterized by the batwing brass.
The Chippendale period (1750-1791) is best characterized by the carved ball and claw foot, the square reeded leg, ogee bracket foot, Chinese design influence and the ribbon back on chairs. The woods of this period were mahogany and walnut. Hardware became more elaborate. Characteristics such as block fronting on chests made pieces more sophisticated and therefore, more valuable.
The Hepplewhite period (1790-1815) is best characterized by the square tapered leg with line inlay, the French foot on chest and the shield or oval back on chairs. The predominate woods in this period were mahogany and walnut with an abundance of inlay. The hardware is best characterized by the oval brass with bale.
The Sheraton period (1795-1815) is typified by round reeded legs and ring turnings. The woods were mahogany, cherry and maple. Hardware ranged from rectangular brasses to rosettes. While this period was named after Thomas Sheraton of London, Duncan Phyfe, a New York cabinetmaker, produced vogue furniture were the saber leg was a dominant trait.
The Empire period (1815-1840) is best characterized by the massiveness of the furniture and the use of mahogany veneer and fancy grained veneer. Legs were generally heavy and the hardware ranged from brass rosettes to glass knobs.
The Victorian period (1840-1900) is the most recognizable by marble top furniture, cabriole legs, and rose carved pieces, particularly sofas. The woods were usually walnut or mahogany.
After the Victorian period, in the twentieth century, there developed two furniture styles worthy of mention, Art Deco and Mission. Mission furniture was made of oak and was very boxy with straight lines. Art Deco is best characterized by heavy veneering and the waterfall design in furniture. These two styles are beginning to enjoy popularity.
Compiled from experience and various sources on the internet, Encarta Encyclopedia and American Heritage Dictionary.