Life places us in a complex web of relationships with other people. Our humanness arises out of these relationships in the course of social interaction. Moreover, our humanness must be sustained through social interaction—and fairly constantly so. When an association continues long enough for two people to become linked together by a relatively stable set of expectations, it is called a relationship.

People are bound within relationships by two types of bonds: expressive ties and instrumental ties. Expressive ties are social links formed when we emotionally invest ourselves in and commit ourselves to other people. Through association with people who are meaningful to us, we achieve a sense of security, love, acceptance, companionship, and personal worth. Instrumental ties are social links formed when we cooperate with other people to achieve some goal. Occasionally, this may mean working with instead of against competitors. More often, we simply cooperate with others to reach some end without endowing the relationship with any larger significance.

Sociologists have built on the distinction between expressive and instrumental ties to distinguish between two types of groups: primary and secondary. A primary group involves two or more people who enjoy a direct, intimate, cohesive relationship with one another. Expressive ties predominate in primary groups; we view the people as ends in themselves and valuable in their own right. A secondary group entails two or more people who are involved in an impersonal relationship and have come together for a specific, practical purpose. Instrumental ties predominate in secondary groups; we perceive people as means to ends rather than as ends in their own right. Sometimes primary group relationships evolve out of secondary group relationships. This happens in many work settings. People on the job often develop close relationships with coworkers as they come to share gripes, jokes, gossip, and satisfactions.

A number of conditions enhance the likelihood that primary groups will arise. First, group size is important. We find it difficult to get to know people personally when they are milling about and dispersed in large groups. In small groups we have a better chance to initiate contact and establish rapport with them. Second, face-to-face contact allows us to size up others. Seeing and talking with one another in close physical proximity makes possible a subtle exchange of ideas and feelings. And third, the probability that we will develop primary group bonds increases as we have frequent and continuous contact. Our ties with people often deepen as we interact with them across time and gradually evolve interlocking habits and interests.

Primary groups are fundamental to us and to society. First, primary groups are critical to the socialization process. Within them, infants and children are introduced to the ways of their society. Such groups are the breeding grounds in which we acquire the norms and values that equip us for social life. Sociologists view primary groups as bridges between individuals and the larger society because they transmit, mediate, and interpret a society's cultural patterns and provide the sense of oneness so critical for social solidarity.

Second, primary groups are fundamental because they provide the settings in which we meet most of our personal needs. Within them, we experience companionship, love, security, and an overall sense of well-being. Not surprisingly, sociologists find that the strength of a group's primary ties has implications for the group's functioning. For example, the stronger the primary group ties of a sports team playing together, the better their record is.

Third, primary groups are fundamental because they serve as powerful instruments for social control. Their members command and dispense many of the rewards that are so vital to us and that make our lives seem worthwhile. Should the use of rewards fail, members can frequently win by rejecting or threatening to ostracize those who deviate from the primary group's norms. For instance, some social groups employ shunning (a person can remain in the community, but others are forbidden to interact with the person) as a device to bring into line individuals whose behavior goes beyond that allowed by the particular group. Even more important, primary groups define social reality for us by structuring our experiences. By providing us with definitions of situations, they elicit from our behavior that conforms to group-devised meanings. Primary groups, then, serve both as carriers of social norms and as enforcers of them.

我们和他人一起生活在一个复杂的关系网中。我们的人性就产生于这种社会性的互动关系中，与此同时，我们的人性也必须通过经常性的社会互动才能得以维持。当两个人在比较稳定的期望值下的交流时间足够长并且形成一种联系时，这种联系就可以称为关系。 人与人之间的关系可以分为两种：情感纽带和工具纽带。情感纽带是当我们做情感投资并致力于他人的一种社会关系。通过和对我们来说十分重要的人交流从而得到安全感、爱情、认同、友谊以及个人价值等一系列情感。工具纽带是我们为达到某种目的而与他人进行合作时产生的社会联系方式。有些时候，这也许意味着变相与竞争者共事。更多的时候我们没有发展出任何更有意义的关系而只是简单的与他人合作达成目的。 社会学家基于情感纽带与工具纽带区别，将社会群体划分成两类：主要群体和次要群体。一个主要群体包含两个以上成员，他们彼此之间的关系是直接的,亲密的,聚合性的。情感纽带在主要社群中起主导作用，我们把人们自身看做目标和人们自己权利的价值。次要群体也是由两个以上成员组成，他们因非个人关系聚到一起都是为了一个特定的,实际的目标而努力。工具纽带在次要群体中起了重要的作用。我们把人自身看做是人目标的途径而不是人们自己权利的目标。有时主要群体的关系也会在次要群体中演化而来。这种现象在工作环境中时有发生。工作伙伴在共事过程中会彼此分享抱怨、玩笑、八卦以及满足感，由此也会发展出亲近的关系。 很多情况也会增加主要群体出现的可能性。首先，群体的规模非常重要。我们很难去了解那些散布在大群体中的某个人。而在小群体中我们有更多机会发起联系并与他人建立关系。第二，面对面的交流能让我们更好地了解彼此。与他人近距离接触和交谈可以更好地交流情感和思想。第三，频繁持续的交流也能增加我们发展主要群体的可能性。我们与他人的联系会随着我们与他人的互动时间而加深，并逐渐演化出连锁的习惯和兴趣。 主要群体是人与人之间乃至整个社会的基础。首先，主要群体在社会化进程中至关重要。在主要群体里，婴儿与孩童可以学习处世方式。这种群体是我们社会生活必备规范和价值的培养地。社会学家将主要群体比作独立个体与整个社会之间的桥梁，因为它能传达,调解并解读一个社会的文化模式，提供一种归属感有助于社会团结。 其次，主要群体之所以是基础是因为它能提供满足我们大多数人需求的环境。在主要群体中，我们可以收获友情、爱情、安全感以及所有幸福的情感。社会学家发现一个群体的主要纽带的强弱往往暗示着这个群体的功能，这不足为奇。例如，一个体育团队的主要群体纽带越强，他们就越容易取得好成绩。 第三，主要群体之所以是基础还因为他们充当了强有力的社会调控工具。群体中的成员掌控并分配能够维持我们生存的极其重要的资源。如果奖励方式不当，群体内成员就会通过拒绝或威胁来摒弃那些背离群体规范的人，例如，一些社会群体采取规避措施（人可以留在群体中，但禁止其他成员与其交流），从而将特定群体中逾矩的个体慢慢同化与他人一致。更重要的是，主要群体通过构筑我们的经验来定义社会现实。他们根据我们的行为来定义我们的处境，以遵循群体分配的意义。因此，主要群体既是社会规范的载体同时也是社会规范的实施者。