Reason - Britannica
Introduction to critical thinking
Rationalism - Columbia Electronic Encyclopedia
Abductive arguments (Khan Academy)
Necessary & sufficient conditions are dealt with briefly in the following video (watch up until 2:55 minutes, when it changes topic)
Sound and unsound arguments (Khan Academy)
Argument and evidence (in relation to religion)
How to argue your case like a great philosopher. Robust debate is an important skill in work and life. Knowing how to argue is more than simply stating your opinion. Dr Patrick Stokes shares his tips.
Critical Thinking - This is a list of YouTube videos explaining many topics including: types of arguments, validity and fallacies etc.
The ENTIRE collection of resources provided by the BBC Birtles Library can be searched on ONE single, powerful search platform, which retrieves print books, eBooks, database articles and websites. Click HERE for assistance.
Stanford Encyclopedia of Philosophy
Internet Encyclopedia of Philosophy
Facts Encyclopedia - Philosophy Resources
Guide to the study of philosophy
Some texts from Early Modern Philosophy
The basics of Philosophy - you can search by branch/doctrine, by historical period, by movement/school, or by individual philosopher.
History of Philosophy - King's College London
Critical Thinking - This is a list of YouTube videos explaining many topics including: types of arguments, validity and fallacies etc.
The Philosopher's Toolkit by 
Philosophy by 