"As opposed to" and "contrary to" in the beginning of sentences

Question

Can I open a sentence with "As opposed to" and "contrary to"? I always heard them in the middle of sentence but not in the beginning of it, and that's why I'm not sure about it.

Examples:

As opposed to what people think, there are not only three states of matter: solid, liquid and gas. But there are four, plasma is additional state of matter.

Contrary to what people think, there are not only three states of matter: solid, liquid and gas, but there are four, since plasma is additional state of matter.

Answer 1

The problem lies partly with the construction of your sentences.

As opposed to doesn't fit well in this context; a fourth state of matter is not opposed to what people may think. That's to say it is not the opposite. To be wrong about something is not necessarily opposed to what is correct. If I say there are three dogs next door when there are four, pointing out the fourth does not oppose my statement. It merely corrects it.

On the other hand contrary to is fine. It fits the context.

However, you could improve the second sentence by changing it to read:

Contrary to what people think, there are not only three states of matter: solid, liquid and gas, but four; plasma is an additional state of matter.

Answer 2

They aren't quite the same.

"As opposed to" usually suggests something is an alternative, for example:

The box is made of plastic, as opposed to wood.

This suggests that some boxes are made of wood, but this box is made of plastic instead. It doesn't in any way deny that other boxes are made of wood.

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"Contrary to" usually suggests an opposite, but also that whatever it is being compared to may be false, for example:

Contrary to opinion, our boxes are made from plastic, not wood.

This means that the boxes are made from plastic, not wood - but also refutes any idea that they were made of wood.

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In answer to your question then - you can open a sentence with "contrary to[x]", because you will immediately go on to state both the incorrect notion and the correct one.

It is not common to open a sentence with "as opposed to". "As" is here being used as an adverb, and while you can open a sentence with an adverb, it is much more common to begin a sentence with the conjunction "as", for example "As it is raining today, we will stay inside". Opening a sentence with "as opposed to" feels wrong to me as an English speaker because of that ambiguity. It isn't clear.