How are familiar name forms such as Tom and Jim created from longer names?

Familiar name forms such as Tom and Jim are known as hypocoristic forms. These are modifications of proper names used in intimate, friendly, or familiar situations.1

These forms are created through several linguistic processes, including:

• Shortening or Clipping: Many familiar names are formed by shortening the original name, such as Tom for Thomas or Jim for James.12
• Alteration: Other forms are created through various modifications of the original name, such as Peggy.2
• Diminutive Affixes: In some cases, names are modified using diminutive suffixes—such as -ie or -y—to indicate familiarity or affection, as seen in names like Bobby or Debbie.3

While these names are often used as informal alternatives, some have become so common that they are frequently used as given names, particularly in the United States. In linguistic terms, these modifications are categorized as diminutives, which can indicate small size or the quality of being familiarly known.12