Comparison with ほうは rather than ほうが


Continuing my mission to understand how people can learn Japanese with
Duolingo (I'm sure it's not possible) I was posed the following sentence:

> My current apartment is more spacious than my previous place.

You are given pieces from which to construct the Japanese equivalent. Without
looking too hard at the pieces given I constructed this sentence:

> 前のアパートより今のほうは広いです。

It irked me that I only had a は and no が among the pieces but I figured that,
given the right context, は would work. I pressed submit only to be told I was
wrong. The official answer was:

> 今のアパートは前の所より広いです。

Past experience shows that Duolingo is reasonably good at accepting
alternative answers, so this leaves me wondering whether there is a problem
with my answer. Does using は really make it unnatural? Perhaps it didn't like
me using ほう instead of 所? Am I missing some other grammar error?




It seems that when you mean "A is more X than B" with the formula AのほうがBよりX,
ほうが is completely a fixed element in this idiom and not replaceable with は.
The argument Bより, however, can be followed by an extra topic particle: ～よりは,
～よりも. Alternatively, using another noun instead of ほう will make the sentence
valid, such as:

> 前のアパートより今のところは広いです。

But it is applying the AはBよりX formula.

Of course, ～のほう can take は when it is not coupled with ～より, even if they
appear in the same sentence.

> （昔の家は実家より狭かったが、）今のほうは実家より広い。

This is also an AはBよりX instance, with ほう intended to contrast with 昔の家.




The sentence 前のアパートより今のほうは広いです has two issues, I think. One being that you are
comparing アパート with 今, rather than with 今のアパート・今のところ, and the second being
that the comparison ～より～のほう, assuming ～のほう is the subject noun-phrase, always
takes the nominative case-marker が. It seems to me that using は with the のほう
comparison is unnatural, since ～のほう already includes the
comparison/contrastive function of は, so marking the subject with が would be
more important. I defer to others, though, since I'm not totally sure.

As you have noted, the official answer does not use the のほう construction, so
using は as a topic and comparison marker is fine.

