Definition:Straightedge

Definition

A straightedge is an ideal tool for constructing straight lines.

A straightedge is of unlimited length, but has no markings on it, so it cannot be used for measurement.

Hence it can be used either:

$(1): \quad$ to construct a line segment between two given points, according to Euclid"s first postulate

or:

$(2): \quad$ to extend a line segment in either direction indefinitely, according to Euclid"s second postulate.

Also known as

The word straightedge can also be rendered as straight edge.

Some sources hyphenate: straight-edge.

Some sources use the term ruler, but this is inaccurate as a ruler is generally understood to have scale markings on it.

Also see

• Definition:Compass and Straightedge Construction

• Results about straightedges can be found here.

Sources

• 1969: C.R.J. Clapham: Introduction to Abstract Algebra ... (previous) ... (next): Chapter $8$: Field Extensions: $\S 40$. Construction with Ruler and Compasses
• 2008: Ian Stewart: Taming the Infinite ... (previous) ... (next): Chapter $2$: The Logic of Shape: Problems for the Greeks
• 2014: Christopher Clapham and James Nicholson: The Concise Oxford Dictionary of Mathematics (5th ed.) ... (previous) ... (next): straight edge