determinants of supply
Just as demand has its shifters, so does supply: the things that change how much sellers will offer at every price. When one of these moves, the whole supply curve slides left or right, and the market price follows — even though the good's own price hasn't changed. These are the levers behind "why did this suddenly get cheaper / dearer when nobody changed the sticker price?"
The main ones cluster around the cost and the count of sellers. First, input prices: when the cost of materials, wages, energy, or rent rises, producing each unit costs more, so supply shrinks (curve shifts left); cheaper inputs do the reverse. Second, technology: a better, cheaper way to make things lets firms offer more at every price (curve shifts right). Third, the number of sellers: more firms entering a market expands supply; firms exiting contracts it. Fourth, taxes and subsidies: a per-unit tax acts like a cost and shifts supply left, while a subsidy shifts it right. Fifth, expectations: if sellers expect a higher price soon, they may hold back today; and for farmed or natural goods, weather, disease, and disasters are powerful, sudden shifters.
As always, the good's own price is excluded — it produces a movement along the supply curve, not a shift, and that is exactly the line to keep clear. A shift in supply changes both the equilibrium price and quantity: a leftward shift (less supply) raises the price and shrinks the amount traded; a rightward shift (more supply) lowers the price and expands it. Predicting a market often comes down to asking which supply determinant just moved, and in which direction — and bear in mind that in the short run supply responds slowly, while over years it can adjust a great deal more.
A drought wrecks the wheat harvest: at every price, far less wheat can be supplied. The supply curve shifts left, bread prices rise, and the quantity traded falls — none of it triggered by wheat's own price.
Weather, costs, technology, taxes, the number of firms — these move supply; the good's own price does not.
A subsidy and a fall in input prices both shift supply right and lower the price — they look identical on the graph, but only one costs taxpayers money. The diagram shows the what; the policy debate is about the who-pays, which the curves alone don't reveal.