Euclid's Elements Book I, Definitions. Level: Middle and High School, SAT Prep, College

Euclid's Book 1 begins with 23 definitions — such as point, line, and surface. Following a visual illustration.

     The first few definitions are:

• Definition 1. A point is that which has no part.

• Definition 2. A line is breadthless length.

• Definition 3. The extremities of a line are points.

• Definition 4. A straight line is a line which lies evenly with the points on itself.