The features that the shoe company builds into their shoes that categorizes them as “neutral”, “stability”, or “motion control” type shoes are intended to be matched up with people based on how much pronation occurs in their feet when they walk or run.
Pronation is a motion in 3 planes, but for the sake of simplifying the discussion to the relationship of pronation and the shoe design, the amount the heel and foot roll inward, from the little toe side of the heel/foot (lateral side) to the big toe side of the heel/foot (medial side), after the foot hits the ground, correlates to the amount of pronation that is occurring. If that amount of pronation is excessive, it is considered "over-pronation". The determination of normal pronation vs. mild, moderate, or severe overpronation is a subject of debate, as there is no consensus on measurable criteria, and is often determined by having an expert examine one's walking or running gait.
A key concept to understand is, unless using an effective orthotic device within the shoe, a foot that over-pronates barefoot still over-pronates within the running shoe no matter what the shoe-type. If the medial side of the foot rolls inward so much that the entire shoe starts to tilt towards that side (valgus tilt) because the mid-sole is compressing down on the medial side, then you need more stability features built into the shoe that you are considering. The reason for this is, on top of the amount your foot is over-pronating within the shoe, additional over-pronation to your foot is being added by the shoe itself, essentially compounding the problem. Furthermore, the midsoles of shoes tend to compress over time where they are getting excessive pressures, which will actually lead to the shoe becoming permanently deformed in shape and broken down on the medial side of the shoe, in valgus alignment, promoting even more over-pronation (Fig. 1). On the other hand, if your shoes are excessively compressing and/or breaking down on the lateral side (varus tilt) when you wear them, you would need shoes with less stability features and more neutral in design. This means your foot is “under-pronating” or “supinating” (opposite of pronating) in the shoe.
Neutral shoes are intended for people who do not over-pronate at all, stability shoes for those who over-pronate mildly to moderately, and motion-control shoes for those who over-pronate severely, or are very heavy individuals who over-pronate moderately. The typical way the shoe is altered, by the shoe designers, to counteract the increased foot pronation is by increasing the density of the midsole of the shoe only on the medial side of the shoe, at the heel and arch area, often seen as a darker colored section of the midsole. If you press in on that section of the midsole, it typically feels firmer than the midsole in the other locations of the shoe (Fig. 2).
Another feature that increases the shoe resistance to over-pronation is an increase in the bulk of the midsole at the medial arch, seen as a reduction in the “carved out” appearance along the medial side of the shoe (again, big toe side). Stiff materials that extend up above the level of the midsole along the medial side of the shoe at the arch and heel along the upper of the shoe can lend additional resistance to over-pronation.
The key to selecting the correct level of stability in your running shoes is making sure that the shoes do not deform in either the direction of valgus (over-pronation) or varus (under-pronation) when your foot impacts the ground and progresses on the ground after foot-strike. This can best be determined by being viewed from behind while walking or running in the shoes. Some running shoe stores will use slow motion video to help in making this determination.