<p>This question makes no sense.</p>

<p>Of course you can make an <em>invalid</em> transaction that doesn't spend an unspent output. If you're fine with calling invalid things transactions, I could just take a piece of random data and call it a transaction.</p>

<p>A <strong>valid</strong> transaction can only spend unspent outputs.</p>

CC BY-SA 3.0
2018-03-19T21:08:29.217Z
Thank you, I think I was getting confused. Your concise answer cleared things up for me.
Kyle Graham
CC BY-SA 3.0
2018-03-19T19:31:27.750Z
2018-03-19T19:31:27.750Z
Pieter Wuille
<p>I was reading this <a href="https://github.com/decentralisedkev/DecentralisedBookRepo/blob/master/decentralised-technology/terminology/deep-dive-utxos.md" rel="nofollow noreferrer">GitHub</a> book on Bitcoin</p>

<p>They state that "True or False: Only UTXOs can be used as inputs to transactions."</p>

<p>Is the answer, True because you can only spend what you have. </p>

<p>Or False, you can out a spent output in the transaction as input, but the network or the miner will reject it.</p>

CC BY-SA 3.0
2018-03-19T17:56:13.607Z
If everyone rejects your transaction, can you call that spending?
alcio
CC BY-SA 3.0
2018-03-19T18:00:28.597Z
@alcio no, you can still use it for an input though right? There's nothing stopping you
Kyle Graham
CC BY-SA 3.0
2018-03-19T18:31:55.487Z
In a technical sense, yes, you are not limited to the UTXO set for inputs, but in a practical sense, you are if you want your transaction to confirm.
alcio
<transactions><utxo>
Is it true that only UTXOs can be used as Transaction Inputs?
Kyle Graham
# Is it true that only UTXOs can be used as Transaction Inputs?

(Asked by: username_0 on 2018-03-19)

I was reading this [GitHub](https://github.com/decentralisedkev/DecentralisedBookRepo/blob/master/decentralised-technology/terminology/deep-dive-utxos.md) book on Bitcoin

They state that "True or False: Only UTXOs can be used as inputs to transactions."

Is the answer, True because you can only spend what you have.

Or False, you can out a spent output in the transaction as input, but the network or the miner will reject it.

**Tags:** transactions, utxo

> **Comments:**
> **username_1**: If everyone rejects your transaction, can you call that spending?  
> **username_0**: @username_1 no, you can still use it for an input though right? There's nothing stopping you  
> **username_1**: In a technical sense, yes, you are not limited to the UTXO set for inputs, but in a practical sense, you are if you want your transaction to confirm.  

---

## 1 answers

### Answer by username_2 on 2018-03-19. Score: 4 | Accepted answer

This question makes no sense.

Of course you can make an *invalid* transaction that doesn't spend an unspent output. If you're fine with calling invalid things transactions, I could just take a piece of random data and call it a transaction.

A **valid** transaction can only spend unspent outputs.

> **Comments:**
> **username_0**: Thank you, I think I was getting confused. Your concise answer cleared things up for me.  

---

