No が in a sentence


If there's no が in a sentence, should I assume that は marks both the topic &
the action-doer? It seems like that's the case every time I encounter
sentences without が.




No. Some easy counter-examples are:

>   * 明日は行きます。  
>  I will go/come tomorrow.
>   * 日本語は話せます。  
>  I can speak (at least) Japanese.
>

