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Easy Introductions to philosophy
Mastering PhilosophyMastering Philosophy by Anthony Harrison-Barbet
Buy new: £11.83 / Used from: £1.50
A more in depth book but looks at a wide range of range subjects
Anarchism: A Very Short Introduction (Very Short Introductions)Anarchism: A Very Short Introduction (Very Short Introductions) by Colin Ward
Buy new: £4.78 / Used from: £5.17
An interesting and easy read.
On Suicide (Penguin Great Ideas)On Suicide (Penguin Great Ideas) by David Hume
Buy new: £3.39 / Used from: £0.03
Small and relatively easy to read essays by Hume on a range of subjects
A Nietzsche Reader (Classics)A Nietzsche Reader (Classics) by Friedrich Nietzsche
Buy new: £5.99 / Used from: £0.01
old but exceptionally handy for browsing through Nietzsche's philosophy. It is also very cheap.
A Rulebook for ArgumentsA Rulebook for Arguments by Anthony Weston
Buy used from: £3.49
An easy read.
The Problem of Philosophy (Great Books in Philosophy)The Problem of Philosophy (Great Books in Philosophy) by Bertrand Russell
Buy used from: £0.90
An easy read, particular if you have had to read mathematical proofs before.
The Essential Nietzsche (Virgin Philosophers)The Essential Nietzsche (Virgin Philosophers) by Paul Strathern
Buy used from: £0.01
These books are short and brilliant. This one is just an example.