Of all philosophers in Western Culture, Aristotle is second only to Plato, and second place may owe much to the fact that, for a time at least, Aristotle was the student of Plato. While some of the specifics of his natural science studies have been proven erroneous in subsequent millenia, his belief, that human beings are capable of observing the world around them and of using logic to understand it, is the very foundation of what we now think of as reasoning (which includes analysis,  critical thinking, and problem solving). Aristotle was the first philosopher of record to propose that the use of systematic categories of things and ideas is the key to understanding not only the world but ourselves. His work on causes is especially illuminating and should sound very familiar to readers.

Aristotle suggested that all things that exist may be usefully analyzed according to their four causes:

Material Cause:	What a thing is made of; its component parts or pieces
Formal Cause:	The shape or format a thing has (including as it comes into being, exists, and then eventually passes out of being)
Efficient Cause:	How a thing works and what it does (its motions and movements)
Final Cause:	Why a thing exists
This is an incredibly helpful way of examining not only things but ideas as well. Consider the causes of Process Education, for instance:
Material Cause:	Process Education (PE) is a performance-based philosophy that is based upon other philosophies of education and which includes emphasis on the continuous development of learning skills through the practice of assessment. (These are its component parts.)
Formal Cause:	The form that PE takes is varied. It can be a classroom, a one-on-one conversation, an individual working alone, or even an internal dialogue. (These are the shapes that PE takes)
Efficient Cause:	PE works only when it is performed or put into practice. As such, any practice which helps a learner to continually develop learning skills through the use of assessment is Process Education at work. (This is how PE works.)
Final Cause:	The whole purpose of Process Education is to produce learner self-development. This is, at base, what we mean when we use the phrase 'student or learner success'. (This is why PE exists as a philosophy/practice.)

The four causes is only one example of the kind of categorical and analytical thinking that Aristotle recommended, but it is immediately apparent how profound his influence has been not only on Western Culture, but upon Process Education, with its assemblage of helpful rubrics, methodologies, classifications and levels. Each of these bears a lasting stamp of Aristotle's genius in teaching us that in order to understand and learn, we must observe, analyze, and THINK in a systematic and logical way.

The majority of Aristotle's works, in English translation, are available at MIT: http://classics.mit.edu/Browse/index-Aristotle.html