Illustrative example: Sensory-logical extrovert ( ) + Intuitive-ethical introvert ( )
ACTIVE WILL - Base function + Suggestive function ( + )
This is the combination that gives duality such a formidable advantage. Around your dual, things make sense. No encouragement or reassurance needed, the duals provide each other with the rest of the picture (where on their own they would be focussed only on half of the picture).
So, in the presence of one anotherm the IEI becomes more grounded in "reality" (by that I mean the sensory world) and the SLE becomes more aware of the dynamic processes that lay behind (and are inseparable from) their sensations.
AUTHORITY - Creative function + Estimative function ( + )
This is where duals activate each other. The estimative function says "I want to ____!" and the dual's creative function replies "You can!".
The IEI wants to understand - the SLE says "You do understand!". They want to substitue their own logic, the SLE thinks this is a very good thing. The SLE wants to create good feelings, the IEI says "You do!". They want to be loved and the IEI is their personal cheerleader.
NEUROSIS - Personal Knowledge + Role function ( + )
This is a point of potential conflict and where subtype becomes very important. The personal knowledge aggressive at best and the role function overly sensitive. Both parties may feel anxious - they want help with their role function but their dual never has an opinion or advice (which is frustrating in itself), and when they do comment it's usually hurtful (though the injured party is undoubtably making too much of the comment).
As a result, usually the intuitive IEI prefers the logical SLE (and vice versa), while the ethical IEI prefers the sensory SLE (and vice versa). One partner will use their base function a little less (and hence their personal knowledge also less!) - much to the delight of their dual's role function - and also will have a little less sensitive role function themselves.
PHOBIA - PoLR + Concrete Art ( + )
This is the point of reassurance and comfort. Partners assert each other's validity.
The IEI lacks insight into their inner states and is prone to feeling "unhuman" as they don't react to things the "right" way. The SLE is the best source of comfort - he has insights into his inner states (Fi is conscious for him) but he considers the whole deal to be over-rated and assures the IEI that it is unimportant and there is no need to worry. Likewise, the SLE lack insight into "accepted" logic and can doubt his own ideas as a result. The IEI assures him that "accepted" logic is unimportant and he is doing fine as he is.
(sorry about the gender, "they" gets confusing after a while)