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Learning scientific concepts
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To learn scientific concepts, one needs to know what one should aim 
for - what it means to have understood a concept.

If you look at worked examples (or at your own solution after you 
found it by trial and error), you need to ask yourself: _Why_ did this 
work here? On which property of the problem did this argument depend? 
How could I recognize when to apply the same trick, argument, 
transformation, substitution, etc., in a different situation? 
and similar questions. 
 
Your understanding is the better the better you can give a running 
commentary on every step of a worked solution (or of a textbook 
presentation of the matter), in a form such as: ''At first <abstract 
action> results in <progress in the written solution>. Then <abstract 
action> leads to <formula in the written solution>. Now the key step is 
to do <abstract action>, reducing the problem to <statement in the 
written solution>.'' etc., in a way that everything is clear to you 
(and to someone listening, if there is one).
 
Learning a concept means learning how it connects to other concepts, 
techniques, tricks, examples that you know already. Science is a very 
dense web of relations, and concepts are nothing else than named 
things expressing such relations. The better connected your web of 
concepts is (and the fewer false connections it has) the better is 
your understanding, and the clearer your perception of what you study.
 
These connection grow mainly by practicing, and by reading the same 
things from as many perspectives as feasible. Therefore instructors, 
textbooks, additional readings, discussions with classmates or in an 
online forum, worked exercises, doing your own exercises, and 
explaining things to others complement each other.