could synthesise
Regular verb: synthesise - synthesised- synthesised

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could synthesise
you could synthesise
he could synthesise
we could synthesise
you could synthesise
they could synthesise 	I could be synthesising
you could be synthesising
he could be synthesising
we could be synthesising
you could be synthesising
they could be synthesising	I could have synthesised
you could have synthesised
he could have synthesised
we could have synthesised
you could have synthesised
they could have synthesised	I could have been synthesising
you could have been synthesising
he could have been synthesising
we could have been synthesising
you could have been synthesising
they could have been synthesising	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't synthesise
you couldn't synthesise
he couldn't synthesise
we couldn't synthesise
you couldn't synthesise
they couldn't synthesise 	I couldn't be synthesising
you couldn't be synthesising
he couldn't be synthesising
we couldn't be synthesising
you couldn't be synthesising
they couldn't be synthesising	I couldn't have synthesised
you couldn't have synthesised
he couldn't have synthesised
we couldn't have synthesised
you couldn't have synthesised
they couldn't have synthesised	I couldn't have been synthesising
you couldn't have been synthesising
he couldn't have been synthesising
we couldn't have been synthesising
you couldn't have been synthesising
they couldn't have been synthesising	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I synthesise?
could you synthesise?
could he synthesise?
could we synthesise?
could you synthesise?
could they synthesise? 	could I be synthesising?
could you be synthesising?
could he be synthesising?
could we be synthesising?
could you be synthesising?
could they be synthesising? 	could I have synthesised?
could you have synthesised?
could he have synthesised?
could we have synthesised?
could you have synthesised?
could they have synthesised? 	could I have been synthesising?
could you have been synthesising?
could he have been synthesising?
could we have been synthesising?
could you have been synthesising?
could they have been synthesising? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I synthesise?
couldn't you synthesise?
couldn't he synthesise?
couldn't we synthesise?
couldn't you synthesise?
couldn't they synthesise? 	couldn't I be synthesising?
couldn't you be synthesising?
couldn't he be synthesising?
couldn't we be synthesising?
couldn't you be synthesising?
couldn't they be synthesising? 	couldn't I have synthesised?
couldn't you have synthesised?
couldn't he have synthesised?
couldn't we have synthesised?
couldn't you have synthesised?
couldn't they have synthesised? 	couldn't I have been synthesising?
couldn't you have been synthesising?
couldn't he have been synthesising?
couldn't we have been synthesising?
couldn't you have been synthesising?
couldn't they have been synthesising?