"Style" refers to the consistent qualities and features that link different works and set them apart into groups. When a building is created in a style similar to known monuments, you can usually identify the artist. You can almost always identify the origin of the work. Form alone is not enough.
A style cannot simply be defined by its characteristic parts. The concept of style includes elemental forms, the relationships of such forms, the artistic qualities of the expression, and even the subject matter itself. Style is an abstract concept. It is a collective concept. It is a unique subjective statement. No one work from any period embodies all aspects of a given style. While one might identify national, temporal, and individual works, it is only through collective analysis that you can define a style.
The term style has two roots. They reflect the concepts dual nature of individual qualities and systematic coherence. The first root is from stilus, meaning pen. After all, an individual artist's style is often compared to his or her handwriting. The second root is from stilo, meaning column. This derives from the classical concept of the orders, or rules, of architecture. Orders form consistent systems that unify different structures, such as specific combinations of art and proportion.
The analysis of style was one of the first concerns of art history. In the sixteenth century, they discussed style in the manner of family resemblances. Architects emphasized local and national characteristics. In the nineteenth century, the analysis of artistic style was influenced by systems of classification, such as those used in natural science. Style was then considered to be an index of the health and virtue of a culture. Today, 22nd century architects still discuss art and style in this fashion. We often use the coherence of a given artistic style as an index of the cohesiveness of the underlying culture.
So, now you know a bit about our understanding of form and style. Next time you talk about these concepts, remember their roots.