The essay that follows will consider Paul G. Hiebert's ideas on cognitive categories and how they may shape our thinking about the church, who is (or who is not) a Christian, and the task of missions.
A. Bounded Sets. This type of categorization emphasizes essential characteristics and uniformity of the characteristics while maintaining a clear boundary separating what is and is not part of the category. Also, the essential characteristics are static, not subject to change. A piece of fruit, for example, must in substance and shape be like every other piece of fruit belonging to the same category; it is or is not a particular kind of fruit, and it will always be the kind of fruit it is until it is consumed or decomposed.
B. Centered Sets. This type of categorization emphasizes defining the center and how things relate to the center (either moving toward or moving away), that things are not uniform as some are closer to the center than others, and that the boundary is not so clear because the main factor is the center and the relationship of the things to it. An example, Hiebert suggests, is a magnetic field: all the particles are in constant motion, but the electrons move toward the positive magnetic pole whereas the protons move toward the negative pole.
C. Fuzzy Sets. This type of categorization emphasizes how things relate to a reference point (or a number of different reference points representing different categories), making the boundary fuzzy. An "either-or" dichotomy is not characteristic of this categorization. A thing may be partly, halfway, or 88% inside a particular set. For instance, a person's race could be an indiscernible mix of Latino, Quiche and African.
A. Christians Defined as Bounded Sets. Uniformity in orthodoxy and orthopraxy is stressed while evangelism is the major task. Conversion is a point in time and when it happens it is based on conscious awareness.
B. Christians Defined as Centered Sets. The center (Jesus Christ as Lord) is clearly defined and Christians are recognized by their relationship to the center (either moving toward or away). There is no uniformity because individuals are at different levels of knowledge and character growth. Legalists might be near the center but moving slowly away, while liberals may be far from the center but moving toward it (Heibert 1979:2-24).
C. Christians Defined as Fuzzy Sets. A person becomes a Christian by degrees. Little would differentiate believer from non-believer. One could be a Christian and yet practice another religion. Hiebert cautions that such an approach raises serious questions (1983:427).
D. Church Defined by Sets. By bounded sets, the church would emphasize evangelism (for bringing people into the church) but less maturation to keep them there (Hiebert 1983:422).
By centered sets, the church would have "a clear division between Christians and non-Christians, but less stress would be placed on maintaining a boundary and more on reaffirming the center in order to preserve the category" (Hiebert 1983:424). Discipleship would stress "the other half of salvation" (Hiebert 1983:424).
By fuzzy sets, the church would condone great theological diversity and probably not even have a membership list. (Hiebert does not explicitly call it for what it is: a paradigm for religious syncretism.)
A. Convert or Disciple. A distinction should be made between convert and disciple. If conversion does not have a precise beginning point, then our gospel is ambiguous. (Baptism as the initiation rite, with all of its accompanying symbolism, no doubt served the early church well in marking the beginning point of salvation.) To be a convert is to be a disciple. Reality shows, however, that not all converts (baptized believers) go on to be disciples (steadfast learners and participants, hearers and doers, in a social context with other believers). It is only for practical reasons that such an artificial distinction is necessary.
B. Salvation as Moment and Process. There is confusion when we distinguish between salvation as a point in time and salvation as a process. There are not two kinds of salvation. There is indeed a specific point in time when salvation begins (getting converted) but the subsequent maturation (getting discipled) should not be regarded as something uniquely different from spiritual growth due to continuance. The apostle Paul, addressing Christians, wrote, ". . . work out your own salvation with fear and trembling," (Philippians 2:12, RSV). He was merely telling the baptized to seriously continue in the faith.
C. Ambiguity Fosters Ambiguity. Today's evangelical doctrine of salvation, emphasizing faith in an isolated manner, has made for some the point of conversion ambiguous. A currently popular missiology handbook propagates the relativism of conversion by its poor explanation of "confession" (Hesselgrave 1980:255-257). It would not be surprising then that some would favor a loose construct for categorizing who is and is not a convert. At the same time, Heibert's favoring of the centered set does not leave room for a clear boundary as regards conversion.
One evangelical, in his analysis of the Great Commission, offered this conclusion, which if followed would bring the "either-or" back to conversion:
Baptism appears as the normal mode of initial confession of Christ. . . . Whether there be saving grace in the act, or with the act, or symbolized by the act is not our concern just now. Baptism needs to be restored to its significance, along with teaching as the means by which one enters upon discipleship and learns how to go about being a good disciple (author's emphasis) (Culver 1967:125).
By recognizing variance, the centered set avoids the dilemma of offering a cheap grace making it possible for the ignorant and gross sinners to become Christians without lengthy periods of training and testing. Growth after conversion is an intrinsic part of what it means to be a Christian. A Christian is not a finished product the moment he is converted (Hiebert 1979:224).Stress on growth also means that every decision a Christian makes, not merely his decision to become a Christian, must take Christ into account. Every decision throughout life moves him toward Christ or slows him down (Hiebert 1979:225).
Hiebert is correct. What would the church profit to convert the whole world but lose its Christianity? However, he does not prove how one method categorizing can apply to both conversion and maturation. Conversion must be unambiguous. Either a person has or has not been converted. This "either-or" aspect requires the bounded set. Maturation is not static. It cannot be a uniform process because no two people are exactly alike. This looseness requires the centered set.
It is no contradiction to use two sets at the same time. Pregnancy can be categorized by both bounded and centered sets. A woman is or is not pregnant--bounded set. She can be progressing in her pregnancy (advancing from the first to second to third trimester) which is a centered set.