Difference between BPD and Narcissism

I've been on this forum for a few weeks and am reading and educating myself about N's. I just ran across this article that certainly overlaps with N's. How would you differentiate? (Maybe in the big picture it doesn't matter as abuse and control and manipulation are the foundation of both.)
------------
Abuse and Borderline Personality Disorder
One of the ways Borderline Personality Disorder manifests is in relationship dysfunction's. Partners of people with BPD are often verbally or emotionally abused by the person who has BPD. Some people with BPD may disassociate during rages; they will honestly not remember the emotional abuse they dish out. Other people with BPD deny having been abusive; inability to accept responsibility for their actions and behavior is a common attribute of BPD. (See Gaslighting below.)

Types of emotional / physical / verbal abuse common in people with BPD:
DOMINATION / CONTROL: The internal chaos of the person with BPD's emotions often gives them a desperate need to control external events, situations and people. (The internal world is so out of control - so external control gives them the sense of stability they lack internally.) They must have their own way, and will resort to manipulation, emotional blackmail,episodes of raging or physical threats to get it. For their partner this creates constant anxiety, fear, erodes self esteem and creates a climate of resentment.

VERBAL ASSAULTS: berating, belittling, criticizing, name calling, screaming, threatening, shaming, excessive blaming, and using sarcasm and humiliation. Blowing the non BP's flaws out of proportion and making fun of the partner in front of others. Over time, this type of abuse utterly erodes the partners sense of self-worth, esteem and confidence.

ABUSIVE EXPECTATIONS: People with BPD generally lack self-soothing skills - they are unable to calm themselves and typically look for this soothing from their partners. The person with BP may place unreasonable demands on their partner and want the partner to put everything else aside to tend to their needs. People with BPD expect that relationships will ease the chronic emptiness they feel, and can become resentful and enraged when the relationship fails to meet their every need. Abusive relationship expectations may include demands for constant attention, frequent sex, a requirement that you spend all your free time with the person, or give up everything else in your life. Because these expectations are based in the chemical / emotional imbalance no matter how much you give, it's never enough. You may be subjected to constant criticism, and are berated because you can't fulfill all this person's needs.

HARASSMENT / STALKING BEHAVIOR: People with BPD lack object constancy. They typically feel that when their partner goes away they will be gone forever. ("Out of sight out of mind.") Non BP's know that "even though ______ is at work right now they still love me." People with BPD cannot reassure themselves that this is so. Partners of people with BPD frequently report that the person with BPD will telephone them 10 -15 times daily to reassure themselves that the partner is still there and still loves them. If the partner is busy or unavailable the person with BPD may become enraged. People with BPD often demand that their partner remain present no matter how abusive the person with BPD becomes; if they can't see their partner they cease to exist for them - triggering deep seated abandonment fears.

EMOTIONAL BLACKMAIL / MANIPULATION: The person with BPD may play on the non BP's fears, guilt, compassion, values, or other "hot buttons" to get what they want. This may include physical threats, withholding affection (the "cold shoulder"), harassment, stalking behaviors, threatening phone messages / email, or use of other threats and / or fear tactics to control the partner.

COMPULSION TO VIOLATE BOUNDARIES: People with BPD often have a compulsive need to violate the boundaries of people and institutions. People with BPD see healthy boundaries in others as limits imposed on them and act out in many ways to assert their control. This manifests as habitual rule breaking, scorn for / resentment of authority figures, petty theft, being asked not to do or say something to you and repeatedly doing it anyway, sexual violation, refusal to honor requests from their partner etc. BP's often unconsciously seek out partners who have difficulty enforcing their boundaries or expressing their anger. This drains the partners energy, makes them feel under constant attack and erodes self-esteem.

UNPREDICTABLE RESPONSES: Drastic mood changes or sudden emotional outbursts (This is part of the definition of BPD). This behavior is damaging because it puts one always on edge. You're always waiting for the other shoe to drop, and you can never know what's expected of you. You must remain hyper-vigilant, waiting for the other person's next outburst or change of mood. This is exhausting and wears down the partner's energy and self esteem.

NOTE: An alcoholic or drug abuser is also likely to act this way. Like all mental health issues, BPD is difficult to diagnose while a person continues to use drugs or alcohol; as it's hard to separate the addictive behavior from symptoms of other disorders. Living with someone like this is tremendously demanding and anxiety provoking, causing the partner to feel constantly frightened, unsettled and off balance.

CYCLING BETWEEN NEED AND RAGE: The person with BPD may cycle rapidly between being very needy and childlike and being rageful and verbally abusive. This is extremely unsettling for their partners becasue you never know what to expect at a given time.

GASLIGHTING: The person with BP will deny your reality and undermine and devalue your perceptions. They will frequently deny that events occurred, lie about their actions and behavior, or deny that they said or did certain things. In some cases this is not a conscious deception. If a borderline has been disassociating,* they may indeed remember what happened very differently. For their partners this is extremely disturbing. It leads them to doubt their own experience, reality and eventually their sanity. Ironically, the partners of BP's often present for treatment first with statements like "I feel like I'm going crazy" or "I don't know what's real anymore."

*Disassociation is a state of not being present, browning out, losing time etc. Some BP's disassociate during episodes of raging. They may have no memory, or only partial memory of things they say or do when angry.

CONSTANT CHAOS / CRISIS MAKING: The person with BPD often seems to be in constant conflict with others. (Neighbors, friends, lovers, co-workers etc.) They may deliberately start arguments for the sake of excitement. Simple problems or issues are frequently blow out of proportion to crisis status. The person wiht BP may be "addicted to drama" since it creates excitement. (Many non-BPs also are addicted to drama.)