P.A. Sorokin has divided groups into major types :

P.A. Sorokin, a well-known sociologist, made significant contributions to the study of social groups. His work on group classification helps us understand the different types of groups that exist in society and how they function. 

Key Points

Sorokin divided the social groups into horizontal and vertical groups.

• Horizontal groups are large, inclusive of groups such as nations, religions, organisation political parties etc.
• Vertical groups are small divisions such as economic classes. Since the vertical group is a part of the horizontal group (the larger group) an individual is member of both.

Hence, the correct answer is Horizontal Groups and Vertical Groups .

Hint

• Involuntary and Voluntary Groups: These refer to groups people join either by choice (voluntary) or by force (involuntary), and distinction made by Dwight Samderson.
• Primary Groups and Secondary Groups: This distinction, made by Charles Cooley, refers to groups based on the intimacy of relationships (primary being close-knit, secondary being more formal and impersonal).
• 'In-Groups' and 'Out-Groups': According to Summer Ingroup is the group with which the individual identifies himself, his family, tribe, sex, college, occupation, religion, etc. by virtue of his awareness of likeness. Outgroup is defined in contrast between 'they' and 'we', like we are democrats and they are communists.