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 Because they require crediting the owner but omit other limitations on the copying, modification, or redistribution of the licensed works, BSD-style licenses are often characterized (with tolerable, if imperfect, accuracy) as “attribution-only” licenses. What the BSD-style licenses omit, moreover, is at least as important as what they require. BSD licenses are not reciprocal licenses and have no “copyleft” condition. Nor do they require source code to be distributed with the software. Because derivatives of BSD-licensed works need not be licensed under a BSD-style license (or any other recognized FOSS license) and need not include source code, BSD-derived code may be freely incorporated into proprietary software works distributed in binary-only form.

3. Open-Source Licensing: Constraint and Liberation
The GPL, the LGPL, and BSD-style licenses serve as useful examples from the broader universe of FOSS licenses because of their very different presumptions and effects. They represent points along a continuum which can be viewed from either of two directions.

The licenses might first be characterized according to the constraining force they exert on downstream users of the licensed works. The BSD license is minimally constraining; beyond the obligations to recognize the original author’s copyright and to refrain from implying endorsement or pro- motion, the license places no limitations on a user’s copying, modification, or distribution of the work, including for profit. At the opposite extreme, the GPL is maximally constraining, regulating not only how a work may be