There are four basic principles of price behavior which have held up over time. Confidence that a type of price action is a true principle is what allows a trader to develop a systematic approach. The following four principles can be modeled and quantified and hold true for all time frames, all markets. The majority of patterns or systems that have a demonstrable edge are based on one of these four enduring principles of price behavior. Charles Dow was one of the first to touch on them in his writings.
Principle One: A Trend Has a Higher Probability of Continuation than Reversal
Principle Two: Momentum Precedes Price
Principle Three: Trends End in a Climax
Principle Four: The Market Alternates between Range Expansion and Range Contraction!