Two systems are used in blockchain networks for processing transactions the fee system and the validation system. These two play different roles in the network.
Fees are the cost of the transaction and how fees work. In the Bitcoin network, fees usually rely on the data size of the transaction and the limited block capacity. The miners can consider these fees when choosing transactions for mining a block. On Solana, the transaction must include a fee paid for in SOL, and an additional priority fee may be used to increase the transaction’s scheduling priority.
Transaction validations verify whether the transactions and blocks comply with the network's rules. For instance, Bitcoin nodes verify the correct spending of outputs in the transaction and compliance with Bitcoin rules in blocks. Solana validators verify the signature, structure, and execution conditions of the transaction.
As the only major distinction between the systems is that fees affect the cost and priority of processing, and validation concerns the compliance with the rules. Therefore, a fee alone cannot make the transaction valid.
Consider the situation when someone transmits a transaction with an appealing fee but is trying to spend the coins he doesn't own. Despite the appeal of such a transaction to the miner, due to the fee rules, the transaction should be still refused because of the Bitcoin validation rules.
In Solana, one can use a priority fee in the transaction, but it will also need to pass all the validations of the network. In case the execution of the transaction is unsuccessful, its state changes are undone, although the fee is charged anyway.
Fees provide the network with economic means of dealing with limited resources of the network, rewarding relevant participants, and limiting the spamming by making transactions too expensive. Validation prevents the network from invalid transactions and unauthorized changes.
Without fee rules, there wouldn't be enough economic instruments of handling the demands of the network and rewarding its participants. Without validation rules, paying users wouldn't be trusted to submit their transactions according to the same rules as the rest of the people.
To summarize, fees help to handle transactions, and validation helps to protect the network from any changes.
