Ockham's razor

Plurality should not be posited without necessity.

Ockham's razor or the law of parsimony (lex parsimoniae) is a problem solving principle devised by William of Ockham, who was an Franciscan friar, scholastic philosopher and theologian.

The principle gives precedence to simplicity: of two competing theories the one with the least assumptions should be chosen.

There are various justifications for Ockham's razor, based on induction, logic and probability theory. But the basic idea behind all can be summed up with 

Fewer assumptions lead to lesser statistical noise (or fewer possibilities of error).

This law can also be applied to software architecture and design by the following rule.

With two competing patterns of implementation, the one with fewer layers or variables should be chosen.

It is important to understand that alternatives need to be fully evaluated in terms of maintainability, performance and future extensibility. If competing alternatives are sufficiently equivalent on these parameters, they can be evaluated by Ockham's razor.

Diagnostic parsimony advocates that when diagnosing a ailment, a doctor should strive to look for the fewest possible causes that account for all symptoms. The same logic could be extended to debugging defects in software. An engineer should look for the fewest possible causes for a defect. This should help in finding the shortest possible path to fixing a defect. And should also help engineers to look at multiple defects at a higher level to see if the defect is caused by a error in implementation or there is a larger impact due to a choice of a design pattern.