Rethinking Judging and Perceiving. This could explain it far better than I can try and sum it up. Great read and maybe, maybe not, enlightening.
http://personalityjunkie.com/03/judging-perceiving-ijs-ips/
But the core is such...(yes, I simply copied and pasted =P)
Extraverts: Since their first extraverted function is also their dominant function, the J-P label aptly describes their dominant mode of functioning.
Introverts: Since their first extraverted function is their auxiliary function, the J-P label belies their dominant mode of functioning.
To better understand these Judging-Perceiving issues, consider the following discussion of the J-P characteristics of the various types:
EPs: EPs might be considered the “purest” Perceivers of all the Myers-Briggs types. Not only do they display Perceiving in their outer behavior and demeanor (e.g., open, adaptable, receptive), but their dominant function (Ne or Se) is also a Perceiving function.
EJs: EJs might be considered the “purest” Judging types. Not only do they display Judging in their outer behavior and demeanor (e.g., assertive, intentional, directive, opinionated), but their dominant function (Te or Fe) is also a Judging function.
IPs: IPs are a mix of J-P characteristics. Since their dominant function is a Judging function (Ti or Fi), they are inner Judgers. IPs are far more serious inwardly than they appear outwardly. Rather than remaining open to new information like healthy EPs, they feel driven to move toward closure and to have things settled in their minds like EJs. They want to hammer down what they believe in order to have a platform from which to make important decisions about their lives. When their beliefs shaken into state of uncertainty, IPs tend to feel unsettled, aimless, and anxious. This anxiety prompts them to avidly locate answers so they can return to a point of comfortable closure and intentional action.
IPs are also like EJs in that they tend to think in terms of what they should be doing. They like to set goals for themselves (especially INPs), even if they rarely end up sticking to them. They tend to approach life with an agenda or a certain set of expectations. Upon waking, they consciously work to determine what they want to/should do and then initiate the process. At least when it comes to initiating tasks, IPs are as disciplined as any EJ.
IJs: IJs are also a mix of J-P characteristics. Outwardly, they look like Judgers. They can be assertive and opinionated, even resembling EJ types. But since their dominant function is a Perceiving function (Ni or Si), they are inner Perceivers. Indeed, they are dominant Perceivers. So in reality, IJs are far less serious, closed, or judgmental than they may appear outwardly.
While IPs are inwardly controlling, IJs inner world is characterized by openness and allowing. Assuming they are not coerced by outside obligations, IJs are not inclined to impose rules or agendas on themselves. Unlike IPs, who start the day with a Judging mindset (Ti or Fi), IJs prefer a more leisurely and perceptive approach (Ni or Si), allowing their Judging process (Fe or Te) emerge organically or spontaneously rather than intentionally. Therefore, when it comes to initiating the Judging process, IJs may procrastinate as long as EPs.