The Elements

6

• A FIGURE is that which is contained by any boundary or boundaries.

Vertical marginal note, likely a summary or commentary on the definitions: A point is... and a line is...

A point is that of which there is no part. that is, nothing A line is a length without breadth. that is, not having breadth

A small dot representing a point.
A short horizontal line segment.

The ends of a line are points. that is, the extremities A straight line is a line which lies evenly with the

A straight horizontal line.

points on itself. that is, ...? A surface is that which has length and breadth only.

A rectangular shape representing a surface.

that is, ...? The ends of a surface are lines. that is, those which contain it A plane
surface is a surface which lies evenly with the straight lines on itself. that is, ...? A plane

A parallelogram-like shape representing a plane surface.

angle is the inclination to each other of two lines in a plane which meet that is, touch one another and are not

Two intersecting lines forming an angle.

placed in a straight line. that is, ...? And when the
lines containing the angle are straight, the angle is called rectilinear.

A rectilinear angle.

that is, named And when a straight line standing on a straight line that is, erected makes the

A diagram showing a perpendicular line standing on another, forming two adjacent angles.

adjacent angles equal to one another, each of the equal angles is a right angle, and the straight line standing

A vertical line standing on a horizontal line, representing a perpendicular (kathetos).

upon that on which it stands is called a perpendicular. that is, ...? An obtuse angle is an angle greater than a right angle. that is, ...?

An obtuse angle.

And an acute angle is one less than a right angle. that is, ...? A boundary is that which is

An acute angle.

the limit of anything. that is, ...? A figure is that which is

A circle with a central point and a single radius line.

contained by any boundary or boundaries. that is, ...? A circle is a plane figure
contained by one line, which is called

A circle with the word "circle" written inside.

the circumference, with respect to which from one point among those lying within

A circle with multiple radii drawn from the center to various points on the circumference.

the figure, all the straight lines falling that is, ...? are equal to one another. And the point is called the center of the circle.

A semicircle diagram.