う・よう + としたがTried to ~ but ~, Was about to ~ but ~, Was going to ~ but ~

As mentioned in our ようとする lesson, when combined with the auxiliary verb う (or よう), とする carries the meaning of 'to try to do (A)', or 'to be about to do (A)'. The case marking particle と in this expression highlights a 'result'.

However, the addition of structures like the conjunction particles が, or たら, to the past tense of する will indicate that something interrupted (A), and therefore it was unable to be completed. In these cases, the translation becomes 'to have tried to do (A), but (B)', 'was about to (A), but (B), or 'was on the verge of (A), but (B)'.

う and よう mark volition (the express intent to do something), while とする adds the nuance that the express intent has been decided, and all that remains is to 'do' the action. Due to this, when something interrupts a ようとする verb, it strongly suggests that (B) is/was highly unanticipated.