1. What do the following words have in common?

SO
UP
CAN
CAP
HER

2. What do the following words have in common?

NOT
POT
LOT
PIN

HINTS:
1. Each word can be followed by the same two letters.
2. Each  word can be followed by the same three letters.

Answers:

1. Each word can be followed by ON:

SOON / UPON / CANON / CAPON / HERON

2. Each word can be followed by ION:

NOTION / POTION / LOTION / PINION