You can't directly use if you are talking about other people's state of mind. You need to attach (which attaches to the root of any i-adj).
> - (I/he/she) swim(s)
> - I want to swim
> - He/she (shows signs that he/she) wants to swim
> - He/she (is showing signs that he/she) wants to swim
For the most part and are pretty similar, just a difference in nuance as to how "current"/"right now" the signs are.
As in your sentence, often the fact that something is happening _now_ is the relevant part, requiring you to use .