話せます and 話します
What is the difference?
Well, for starters, both are different inflections of the verb 話す, which means "To speak". The first one you typed, 話せます, is the potential form with polite ending, meaning " can speak". The second one, 話します, is exactly the same as 話す ("To speak"), only using the polite ending ~ます.
- I speak Japanese. = 私は日本語を話す (standard)
- I speak Japanese. = 私は日本語を話します (polite ending)
- I can speak Japanese. = 私は日本語を話せます (potential form, polite ending)
Also, the potential form without using the polite ending would be 話せる。
- I can speak Japanese. = 私は日本語を話せる (potential form, no polite ending)
が is used with nouns and adjectives. を is used with verbs.
話せる, the ability to speak, should generally take が as potential verb forms are intransitive and do not take a direct object.
話す is a transitive verb so takes を
Though not standard, it is not entirely uncommon to see potential form verbs using を instead of が. Using が puts more emphasis on the language that is being spoken whereas を shows more volition in the ability to speak. The active decision and work of being able to speak rather than a natural ability to.
The example sentences that Duo uses for potential form take が
話します means “speak”, and 話せます means “can speak” or “is able to speak “