An explanation has a cause, a mechanism and an effect, linked by words such as because, so and therefore. A description has only the effect.
This page supports the SPM Economics learning guide. The lesson version is writing cause, mechanism and effect explanations.
What does this look like for you?
You write, “The supply curve shifts to the left and the price goes up.” The feedback says “describes, does not explain”. You point at the graph and say it is all there, yet the marker wanted something the graph cannot show.
What usually causes it?
- The cause is left out because it seems obvious.
- The mechanism, meaning the step between the cause and the curve, is skipped.
- The effect is stated as a shape: “goes up”, “moves right”.
- The sentence has no link word, so the ideas sit side by side without connection.
A cause, mechanism and effect template
Use three short clauses:
- Because (the cause): what changed.
- So (the mechanism): how that changes behaviour or cost, and which curve moves.
- Which leads to (the effect): the new price and quantity.
A worked rewrite
A fictional stall sells fried rice. The price of cooking oil rises.
Draft 1, description. “The supply curve shifts to the left and the price rises.”
Draft 2, a cause added. “Because the price of cooking oil rises, the supply curve shifts to the left and the price rises.”
Draft 3, full chain. “Because the price of cooking oil rises, the cost of each plate of fried rice increases. At each price, the stall is willing to sell fewer plates, so supply shifts to the left. At the old price, buyers now want more plates than are offered, which pushes the price up and reduces the quantity sold.”
Draft 3 has a cause, a mechanism that explains why the curve moves, and an effect on both price and quantity. The move from draft 2 to draft 3 is the “so”, which is the part most students leave out.
Check a draft in 30 seconds
| Question | If the answer is no |
|---|---|
| Is there a cause in the first clause? | Add “because” and state what changed |
| Is there a reason the curve moves? | Add “so” and link cost or behaviour to the curve |
| Are both price and quantity named? | Add the missing one |
| Is there at least one link word? | Add “because”, “so” or “which leads to” |
A shorter form uses the same three parts. “Dearer oil raises the stall’s cost, so it sells fewer plates at each price, which raises the price and lowers the quantity.” For help putting this into words when you are looking at a diagram, see explaining an Economics diagram in words.
What can I do this week?
Pick three of your old answers marked as description. Rewrite each in the because-so-which pattern. Use the claim, evidence and explanation revision desk to compare your draft with the checklist above, and log the missing link in the mistake log.
When might one-to-one tuition help?
If you can name the cause but cannot find the mechanism sentence, a teacher can ask you the question “why would the seller do that?” until the sentence appears. That back-and-forth builds the habit in a way a model answer cannot.
Read about online one-to-one Economics tuition, or the one-hour trial class (from RM50), which is a real taught lesson.