September, October, November and December sound like numbers 7, 8, 9 and 10, but they are months number 9, 10, 11 and 12, because the old Roman year started in March and the list changed later.
First, what do the names mean?
The names come from Latin number words:
septem = seven → September
octo = eight → October
novem = nine → November
decem = ten → December
You can hear the numbers in other English words too: octopus (eight legs), decade (ten years) and octagon (eight sides).
The weird part
Count them on a calendar:
September is month 9, not 7.
October is month 10, not 8.
November is month 11, not 9.
December is month 12, not 10.
Every one is two numbers off. English kept the old number names but moved the months.
What happened?
In the old Roman calendar, the year started in March. Count from March and the names fit:
March = 1, April = 2, May = 3, June = 4, July = 5, August = 6
September = 7, October = 8, November = 9, December = 10
So the names were right for the old order. The order changed, but the names stayed the same.
How did the year move?
People do not agree on one answer, so here are the two ideas:
- A short old calendar. Some writers say the early Roman calendar had only ten months, and January and February were added later. Some historians think this may have been a later way of explaining the names.
- A moved start. Others say the Romans always had twelve months, and the new year moved from March to January 1. One note says the top Roman officials began their year on January 1 from 153 BCE.
Either way, the month names did not move with the start of the year. The calendar changed, and the old numbers stayed in the names.
🗣️ Natural Examples
My birthday is in September, the ninth month.
We go on a trip every October.
November days are short.
December is the last month of the year.
I can say all four months in order.
⚠️ Common Mistakes
Do not use the number names as dates.
❌ September is month seven.
✅ September is month nine.
Spell them with the right ending.
❌ Septembre, Decembre
✅ September, December
Months start with capital letters.
❌ We start school in september.
✅ We start school in September.
💬 In a Conversation
Sam: September starts with sept. That means seven, right?
Mia: It does. But September is the ninth month.
Sam: So who counted wrong?
Mia: The Romans counted from March.
Sam: Then the calendar moved and the names stayed. Typical.
⏳ The OddLingo Timeline
Old Roman year: starts in March
↓ September = 7th, October = 8th, November = 9th, December = 10th
↓ January and February move to the start of the year
↓ the months shift two places later
↓ today: the names still say 7, 8, 9 and 10, but the months are 9, 10, 11 and 12
🥡 The OddLingo Takeaway
The month names are fossils. They are old number words that stayed after the calendar moved. If you forget a month's real number, add 2 to the number in its name.
For another case where English keeps an old pattern, see eleven and twelve.