Step 1: Understanding the Concept:
Jain substances are classified based on their spatial extension. Those that occupy multiple units of space (Pradeshas) are called Astikayas. Those that do not have an extended body are non-astikayas.
Step 2: Detailed Explanation:
1. Astikayas: Jiva, Pudgala, Dharma, Adharma, and Akasha occupy many space-points. For instance, a soul can expand or contract to fit its body.
2. Kala (Time): Time is made of discrete units called Kalanus (time-atoms). These atoms are scattered throughout the universe (Lokakasha).
3. Spatial Limitation: Each time-atom occupies exactly one Pradesha (one point of space) and does not combine with other time-atoms to form a multi-point structure.
4. Conclusion: Because a time-atom is limited to a single space-point at any given time and lacks spatial extension, it is called Ekapradeshi. It is the only substance among the six that is NOT an Astikaya.
Step 3: Final Answer:
Time (Kala) is the only Ekapradeshi substance.