What is the difference between parenthesis and no parenthesis in head and tail?

[kulimer]

My first week using Python. I am a little confused about if I should use parenthesis or not when doing head and tail

Suppose I have variable df as a data frame in NumPy

df.head vs df.head() vs df.head(5) 

I understand the 5 means show first 5 rows, but how do I know if I should use df.head or df.head(), though df.head() gives me what I want.

But, why the following. This would be correct

df.column

This

df.column()

would give me an error message.

Why such inconsistency? I am so confused!