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Logic is a fundamental aspect of mathematics and philosophy. It is the study of valid reasoning, where we use various rules and principles to determine the truth-values of statements. In logic, each statement must be either true or false, but not both.

For example, consider the statement 'All humans are mortal'. This is a logical statement because it can be proven true based on evidence and understanding. These true or false values are what help us build arguments and understand relationships between different statements.

In logical systems, consistency is key. If a system contains a contradiction (like a statement being both true and false), it breaks the logical structure, making reasoning within that system unreliable.

Statements in logic are sentences that declare something and must have a truth value of either true or false. These are essential in constructing logical arguments and proofs.

To better understand, let's look at some examples:

• 'The sky is blue.' This is a statement because it clearly can be proven true or false based on observation.
• 'She is smart.' Here, it's more complex since 'smart' can be subjective, but within a specific context with defined criteria, it may be considered a logical statement.

Statements form the foundation of logical reasoning. Without them, we wouldn't be able to systematically deduce new information from what we already know. For a sentence to be a logical statement, it must be unambiguous and clear, allowing for no room for it to be both true and false at the same time.

A self-referential paradox is a statement that refers to itself in a way that creates a paradox, meaning it cannot consistently be either true or false.

The most famous example is the 'Liar Paradox', which is the sentence 'This sentence is false.' If this statement is true, then it must be false, since it states that it is false. Conversely, if it is false, it must actually be true, because it claims to be false.

Such paradoxes challenge our understanding of truth and consistency in logical systems. They show that not all sentences can neatly fit into being either true or false. In logic, this is important because it indicates boundaries and limitations within each logical framework. Understanding these paradoxes helps us refine our understanding and approach to logical theory.