You already know about Cardinal Utility, which tries to measure satisfaction with a specific number, like '10 utils' from a cup of tea. But how do you really measure happiness? It's tricky. The Ordinal Utility approach offers a more practical alternative. It argues that while we can't measure satisfaction, we can certainly rank our preferences. You know if you prefer a samosa over a kachori, even if you can't say by exactly 'how much'.

This shift from measuring to ranking is the core of ordinal theory. It doesn't need to know the 'amount' of utility, just the order of preference. This makes it a more realistic way to look at consumer choices. To build this theory, economists rely on a few basic assumptions about how a rational person behaves. These are often called the axioms of preference.

For ordinal utility to work, we assume consumers are rational. This isn't about making the 'best' life choices, but about being consistent. This consistency is defined by three simple rules, or axioms.

1. Completeness: This axiom states that for any two bundles of goods, say Bundle A (2 bananas, 1 apple) and Bundle B (1 banana, 2 apples), a consumer can make a comparison. They must be able to decide one of the following:

• They prefer A to B.
• They prefer B to A.
• They are indifferent between A and B (both would give them the same level of satisfaction).

A rational consumer is never stumped. They can always compare two options. This ensures that every possible choice can be placed in a preference ranking.

2. Transitivity: This is the axiom of logical consistency. It says that if you prefer Bundle A to Bundle B, and you prefer Bundle B to Bundle C, then you must prefer Bundle A to Bundle C. It's like saying if you prefer coffee over tea, and tea over juice, then you must prefer coffee over juice.

Without this rule, preferences would be circular. You might prefer A to B, B to C, but C to A. This creates a loop where no best choice can be identified. Transitivity ensures our preferences can be ordered in a straight line, not a circle.

3. Non-satiation (or Monotonicity): This one is simple: more is better. It assumes that a consumer will always prefer a bundle that has more of at least one good and no less of the other. If Bundle A has 2 bananas and 2 apples, and Bundle B has 2 bananas and 1 apple, you will always prefer Bundle A. You are never 'full' or 'satiated' to the point where an extra item makes you less happy.

This assumption guarantees that consumers always want to consume more, which is a key driver of economic activity. It also shapes the indifference curves we will study later.

These three axioms together form the foundation of rational choice theory. They allow economists to model consumer behaviour in a predictable way, assuming that people make logical and consistent decisions to maximise their satisfaction. This lays the groundwork for understanding indifference curves.

So, what's the big picture? The ordinal approach frees us from the impossible task of putting a number on happiness. Instead, it focuses on what we can observe: the choices people make. By assuming that preferences are complete, transitive, and that more is better, we can build a logical framework. This framework, based on monotonic preferences, is crucial for analysing how consumers react to price and income changes without needing to know anything about 'utils'. It's the starting point for a more nuanced understanding of demand.

This foundation allows us to graphically represent preferences using indifference curves, which are our next topic. Each curve will show combinations of goods that provide the exact same level of satisfaction, a concept that relies entirely on these three core assumptions.

Time for a quick check on these foundational ideas.

Let's see if you've mastered the axioms.

Understanding these assumptions is the key to unlocking consumer behaviour analysis. They provide the logical structure upon which everything else is built.