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I was wondering when to use which because both optimal and ideal convey the same meaning to me.

For e.g., comparing these two usages:

  1. This is the optimal temperature for the machine to work correctly.
  2. This is the ideal temperature for the machine to work correctly.

When referring to people, I do generally use ideal, e.g.

He is an ideal husband.

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6 Answers 6

up vote 13 down vote accepted

The meanings are similar:

Optimal: Best or most favorable; optimum

Ideal: Satisfying one's conception of what is perfect; most suitable

In my mind optimal is the best that is reasonably possible while ideal is the perfect and possibly unattainable.

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I agree: I'd generally use optimal in situations where a thing was reasonably attainable and fairly likely, ideal where it might be possible but it's not very likely. –  Matthew Frederick Sep 8 '11 at 9:27
    
+1 I have to agree with this. Very succintly put Coomie –  Thursagen Sep 8 '11 at 20:06
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"Optimal" seems to convey the impression, to me, that the temperature is the best, at the moment, but it's not the ideal. That is, under the current/surrounding circumstances, the temperature that is optimal would be... etc.

"ideal", is stating a temperature that would be perfect, but this doesn't mean that this temperature is achievable in all circumstances, and it sometimes can't be achieved at all.

Edit:, Able to confirm the usage and definition of "optimal":

The best, most favourable or desirable, especially under some restriction

As you can see, there is a restriction. That is, "optimal" is used when referring to the best possible ...whatever... under certain restrictions, such as the environment, or the conditions surrounding the time of occurrence.

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Yep, constraints make a difference. –  Ben Voigt Sep 10 '11 at 5:48
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Optimal takes more than one variable in consideration and looks at the total result (of two or more variables) while ideal may look at one variable and disregard the other/s.

Example: to create automation you build the functionality that automates the manual process (development cost) and then you apply the automation in production (operational improvements).

  • An ideal operational improvement is building a solution that will create the lowest operational costs (not consider development costs).
  • An optimal operational improvement is finding a balance between development cost and ideal operational improvement where when adding the total development costs and total operational savings, it equals the biggest total savings. May not be the ideal operational solution (looking from the operational perspective alone) but it is optimal taking all other variables in consideration.
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While this isn't required by their definitions, I think there's a noticible difference in how they tend to be used:

  • "Optimal" is more often used to describe things that can be measured, like a single variable or permutation of variables. It tends to be tactically actionable.
  • "Ideal" tends to be used to describe more conceptual, strategic goals, where what you'd actually optimize to achieve it is hard to define or highly complex.
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To my mind, these international words,existing in many European languages, can by synonyms in some cases, but, as we know, there are no absolute synonyms in language : Optimal- that's the best possible under certain circumstances in reality (it can be with even some irreparable drawbacks), and Ideal means the best that can ever be under any circumstances and ever exist.

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From the Shorter Oxford English Dictionary:

Ideal: Conceived as perfect in its kind

The Dictionary doesn't have optimal, but only

Optimum: Best or most favourable

This connection between optimal and optimum is also backed up by Dictionary.com, where the first term is referred to the latter.

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