It depends what you mean. 'I see my brother shaves' can make sense, but means something different to 'I see my brother shave' or 'I see my brother shaving'. For example, if you had not seen your teenage brother for a while you might see evidence that he has started shaving and say 'I see my brother shaves!' meaning 'It is obvious to me that my brother shaves', not 'I see him engaged in the act of shaving'

Present (action in progress) My brother is shaving. I see my brother shaving. Past (action in progress) My brother was shaving. I saw my brother shaving. Past (completed action) My brother shaved. I saw my brother shave. [shave, not shaveD; = I saw him shaving from beginning to end.] Habit My brother shaves every morning. I see my brother shave every morning. [shave, not shaveS] More information: Practical English Usage 3rd edtion by Swan, section 411-7 participles (4) object complements excerpt The structure "object + participle (clause)" is used after verbs of sensation (e.g. see, hear [...]) and some other verbs (e.g. find, get, have, make). I saw a small girl standing in the goldfish pond. Have you ever heard a nighingale singing? [end excerpt] For the past, there is a choice of describing an action in progress or a completed action. More information here: https://dictionary.cambridge.org/grammar/british-grammar/hear-see-etc-object-infinitive-or-ing [excerpt] We can use either the infinitive without to or the -ing form after the object of verbs such as hear, see, notice, watch. The infinitive without to often emphasises the whole action or event which someone hears or sees. The -ing form usually emphasises an action or event which is in progress or not yet completed.

It would be the first one. Another way this is commonly said is " I'm watching my brother shave" or for the past tense, "I have seen my brother shave." I hope this helps!

It would be the first one. Another way this is commonly said is " I'm watching my brother shave" or for the past tense, "I have seen my brother shave." I hope this helps!