<p>The definition in the theory of codes does not require the alphabet to have two or more symbols, see for example the textbook by <a href="http://lipn.univ-paris13.fr/~duchamp/Books&amp;more/Berstel/%5BJean_Berstel,_Dominique_Perrin%5D_Theory_of_Codes_((BookFi.org).pdf" rel="nofollow noreferrer">Berstel and Perrin</a>. Over a one-letter alphabet the only codes are exactly the one-word sets. So mathematically this is not as interesting as bigger alphabets.</p>

<p>If your symbol can have different intensities, the most obvious way of formally modelling is to use different symbols for the different intensities. With this you would end up with a code over a bigger alphabet.</p>

CC BY-SA 3.0
2017-07-22T13:04:45.313Z
thanks Peter. do you have  a specific part of that book in mind?
magnolia1
CC BY-SA 3.0
2017-07-22T13:34:16.030Z
The definition of code is on page 37, @matteoeoeo.
Peter Leupold
CC BY-SA 3.0
2017-07-22T09:35:48.637Z
2017-07-22T09:35:48.637Z
Peter Leupold
<p>I am wondering whether you could still call a code something that, if transmitting, only transmits one symbol. Or does the formal definition of code require 2 or more symbols? (and would the answer change if that symbol can have different intensities, so perhaps having 2 or more intensities makes this a code?)
thanks!</p>

<it.information-theory><coding-theory><encoding><shannon>
Does a code need at least two symbols to be defined as a code?
magnolia1
# Does a code need at least two symbols to be defined as a code?

(Asked by: username_0 on 2017-07-22)

I am wondering whether you could still call a code something that, if transmitting, only transmits one symbol. Or does the formal definition of code require 2 or more symbols? (and would the answer change if that symbol can have different intensities, so perhaps having 2 or more intensities makes this a code?)
thanks!

**Tags:** it.information-theory, coding-theory, encoding, shannon


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## 1 answers

### Answer by username_1 on 2017-07-22. Score: 0 | Accepted answer

The definition in the theory of codes does not require the alphabet to have two or more symbols, see for example the textbook by [Berstel and Perrin](http://lipn.univ-paris13.fr/~duchamp/Books&more/Berstel/%5BJean_Berstel,_Dominique_Perrin%5D_Theory_of_Codes_((BookFi.org).pdf). Over a one-letter alphabet the only codes are exactly the one-word sets. So mathematically this is not as interesting as bigger alphabets.

If your symbol can have different intensities, the most obvious way of formally modelling is to use different symbols for the different intensities. With this you would end up with a code over a bigger alphabet.

> **Comments:**
> **username_0**: thanks Peter. do you have  a specific part of that book in mind?  
> **username_1**: The definition of code is on page 37, @matteoeoeo.  

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