'Justified' is a word in the past tense. That means that it is used to refer to events from the past. The infinitive form of 'justified' is 'justify'. To justify is to show to others that something that was done was right, that it was reasonable, given the situation. It almost brings to mind the need to defend one's decisions when one's motives are put into question. For example: 'Joe's decision to move out of London was justified.' This sentence shows us that the speaker thinks that Joe's decision to move out of London was wise. He agrees with Joe and if the speaker was in the same situation, they would probably do the same. The word 'justified', however, gives this sentence a definitive tone. Using 'justified' implies that what Joe did was most certainly right and correct, and that his motives for moving out of London are absolutely valid. It is as if a group of judges met and discussed what Joe did, and they decided that his decision was 'justified', that Joe had good reasons to decide to move out and what Joe did was absolutely right, and what he did never has to be discussed again. 'Justifiable' though, has a bit of a different meaning. 'Joe's decision to move out of London was justifiable'. A synonym for the word 'justifiable' is 'understandable'. 'Justifiable' means that if something was to be called into question, like someone's motives or actions, it would turn out to be justified. Using the example from the previous paragraph, if 'Joe's decision to move out of London was justifiable', then the judges haven't yet met to assess Joe's actions, but if they did, they would find that Joe had valid reasons for doing what he did. So 'justifiable' is less definite and not as strong as 'justified'.

Thank you Brock!

Assuming you already know the meaning of 'Justify': Justifiable is something that CAN BE 'Justified'. "His decision is justifiable." Justified is something IN THE PAST. "His decision was justified because of...[enter reason here]." Hope this helps?! :)