Actually, supposably is a word. It’s the adverb form of the word supposable, meaning capable of being supposed or imagined.
I don’t understand why people get so upset about these things. Every word we use was not a word before somebody started using it. That’s how language works (at least the English language, that is.) Dictionaries are rewritten every year to catch up with the way people talk. It’s not like lexicographers write dictionaries first and then mandate how every one else should speak and write.
The pronunciation of “ask” has been going back and forth between something which sounds like the current standard pronunciation of “ask” and the dialectal pronunciation which sounds something like the current standard pronunciation of “ax” since at least the time of Old English, more than a thousand years ago:
The pronunciation of “height” with a “th” sound at the end also goes back a long way:
People have this bizarre notion that the vocabulary, pronunciation, and grammar used in nonstandard dialects are strictly modern things. They have the bizarre notion that such vocabulary items, pronunciations, and grammatical uses must have evolved just recently from the standard language. This isn’t remotely true. All languages have had a variety of dialects throughout their histories. There have been influences going back and forth between standard and nonstandard dialects throughout their histories.
To go back to the point I was trying to make three and a half years ago, a nonstandard dialect counts as a “language” and the words in it count as “words.” A language (and any dialect of it) is anything used by humans for ordinary communication. The units of any such language or dialect are words. If you want to ask if a particular word, pronunciation, or grammatical item is a part of standard English, then say so. This is important for determining if you’re going to get marked down on a paper by your high school English teacher or corrected by a copy editor for an article or book or told to change your pronunciation by the producer of a national news show (if you’re the anchor of the show).
It is not important though for ordinary conversation between people in most circumstances. If you go around correcting other people’s vocabulary, pronunciation, and grammar in ordinary conversations, eventually someone is going to punch your lights out. There are occasions where two people in a conversation speak such different dialects that they may have trouble understanding each other. In that case they will have to work something out. In most cases you should never try to imply that the other speaker in a conversation is stupid and/or ignorant for using their own dialect.
It is currently considered non-standard by most entities which try to create standards for usage.
The purpose of standardization is to slow down the evolution of language enough so that on average clear communication is retained. A secondary effect of this is that standard usage tends to be a shorthand way of separating the educated from the uneducated.
When you say “heighth” you are communicating the concept accurately, but you also communicate that you are either unaware it is non-standard, or do not care. Both convey something beyond the word itself.
Since the evolution of language is driven by the masses, it can be argued that any non-standard use is simply usage ahead of its time.
But mostly non-standard usage conveys ignorance until such time as the non-standard usage gets driven so broadly that “correction” against standard usage slips over from being useful into pedantry.
It’s best to just check with me about where that line is, but I am usually too busy to address specific concerns.
However, your assertion does not make “supposably” a synonym or alternate pronunciation for “supposedly.” Which seems to me to be the predominant use of “supposably.”
Like “pskeddy” as an alternate pronunciation for “spaghetti”, IMO it’s simply lisping child-speak carried over into adulthood. IMO it is almost never someone intending to communicate “capable of being supposed or imagined.”
And FWIW, the spell check in my browser doesn’t like “supposably” either.
The difference between “supposably” and “supposively” is that the former is the adverb to an indubitably existing adjective, “supposable”. Hence, it can be used in any sentence where an adverbial form of this adjective is needed, and will in such a sentence without any doubt be correct. “Supposively”, however, would have to be the adverbial form of an adjective “supposive”, which does not seem to exist. Which does not mean, of course, that it cannot come into existence some stage in the future if the everyday practice of English-speaking people develops in a directuion that includes the word. It’s a little bit like the process of forming customary law. There is no central planning authority defining what should and what should not be a word, it’s rather the uncoordinated practice of many, many people and the way they speak, the totality of which is called “the English language”. There is no other reasonable way of defining “the English language” but to say that it is whatever English-speaking people have consented on to use for their communication.
