Optical relates to sight, light and lenses. Optimal means best possible. An optical illusion; the optimal route. The c and the m are the only difference on the page; the eye and the best are the difference underneath.
The core difference
- optical — of vision or light; using light. Optical fibre, an optical illusion, optical character recognition.
- optimal — the best achievable under the circumstances. Optimal conditions, the optimal dose, far from optimal.
The tell
Optical goes with optician and optics — the eye. Optimal goes with optimum and optimise — the best. An optical solution would be one made of lenses; an optimal one is simply the best available. Anything with light in it is optical; anything with a target in it is optimal.
In use
- optical — The drawing is an optical illusion — the lines are the same length. Data travels down the optical fibre as light.
- optimal — Twenty degrees is the optimal temperature for the yeast. The schedule is not optimal, but it works.
Common slips
- an optimal illusion → an optical illusion
- the optical solution (meaning the best) → the optimal solution
Optical is the eye; optimal is the best.
Where the words come from
Optical is from Greek optikos, "of sight", from ops "eye" — the root of optician and autopsy. Optimal is from Latin optimus, "best", the superlative of bonus "good" — the root of optimism, the belief that things are for the best.
